diff --git a/.github/workflows/go.yml b/.github/workflows/go.yml
index 0df9133..414c525 100644
--- a/.github/workflows/go.yml
+++ b/.github/workflows/go.yml
@@ -1,25 +1,50 @@
 name: build
-on: [push, pull_request]
-jobs:
 
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+
+jobs:
   test-build:
     name: Test & Build
     runs-on: ubuntu-latest
     steps:
 
-    - name: Set up Go 1.15
-      uses: actions/setup-go@v1
+    - name: Set up Go
+      uses: actions/setup-go@v2
       with:
-        go-version: 1.15
-      id: go
+        go-version: ^1.17
 
     - name: Check out code into the Go module directory
-      uses: actions/checkout@v1
+      uses: actions/checkout@v2
+
+    - name: Run go mod tidy
+      run: |
+        set -e
+        go mod tidy
+        output=$(git status -s)
+        if [ -z "${output}" ]; then
+         exit 0
+        fi
+        echo 'We wish to maintain a tidy state for go mod. Please run `go mod tidy` on your branch, commit and push again.'
+        echo 'Running `go mod tidy` on this CI test yields with the following changes:'
+        echo "$output"
+        exit 1
       
     - name: Test
       run: |
-        go mod tidy -v
         go test -race ./...
 
+    - name: Go vet
+      run: "go vet ./..."
+
+    - name: Staticcheck
+      uses: dominikh/staticcheck-action@v1.1.0
+      with:
+        version: "2021.1.1"
+        install-go: false
+
     - name: Build
       run: go build ./...
diff --git a/internal/gomodifytags/gomodifytags.go b/internal/gomodifytags/gomodifytags.go
new file mode 100644
index 0000000..a174323
--- /dev/null
+++ b/internal/gomodifytags/gomodifytags.go
@@ -0,0 +1,801 @@
+package gomodifytags
+
+import (
+	"bufio"
+	"bytes"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"go/ast"
+	"go/format"
+	"go/parser"
+	"go/printer"
+	"go/token"
+	"io"
+	"io/ioutil"
+	"sort"
+	"strconv"
+	"strings"
+	"unicode"
+
+	"github.com/fatih/camelcase"
+	"github.com/fatih/structtag"
+	"golang.org/x/tools/go/buildutil"
+)
+
+// structType contains a structType node and it's name. It's a convenient
+// helper type, because *ast.StructType doesn't contain the name of the struct
+type structType struct {
+	name string
+	node *ast.StructType
+}
+
+// output is used usually by editors
+type output struct {
+	Start  int      `json:"start"`
+	End    int      `json:"end"`
+	Lines  []string `json:"lines"`
+	Errors []string `json:"errors,omitempty"`
+}
+
+// Config configures gomodify tags and describes how tags should be modified.
+type Config struct {
+	fset *token.FileSet
+
+	File     string
+	Output   string
+	Quiet    bool
+	Write    bool
+	Modified io.Reader
+
+	Offset     int
+	StructName string
+	FieldName  string
+	Line       string
+	Start, End int
+	All        bool
+
+	Remove        []string
+	RemoveOptions []string
+
+	Add                  []string
+	AddOptions           []string
+	Override             bool
+	SkipUnexportedFields bool
+
+	Transform   string
+	Sort        bool
+	ValueFormat string
+	Clear       bool
+	ClearOption bool
+}
+
+// Run runs gomodofiytags with the config.
+func (c *Config) Run() error {
+	err := c.validate()
+	if err != nil {
+		return err
+	}
+
+	node, err := c.parse()
+	if err != nil {
+		return err
+	}
+
+	start, end, err := c.findSelection(node)
+	if err != nil {
+		return err
+	}
+
+	rewrittenNode, errs := c.rewrite(node, start, end)
+	if errs != nil {
+		if _, ok := errs.(*rewriteErrors); !ok {
+			return errs
+		}
+	}
+
+	out, err := c.format(rewrittenNode, errs)
+	if err != nil {
+		return err
+	}
+
+	if !c.Quiet {
+		fmt.Println(out)
+	}
+
+	return nil
+}
+
+func (c *Config) parse() (ast.Node, error) {
+	c.fset = token.NewFileSet()
+	var contents interface{}
+	if c.Modified != nil {
+		archive, err := buildutil.ParseOverlayArchive(c.Modified)
+		if err != nil {
+			return nil, fmt.Errorf("failed to parse -modified archive: %v", err)
+		}
+		fc, ok := archive[c.File]
+		if !ok {
+			return nil, fmt.Errorf("couldn't find %s in archive", c.File)
+		}
+		contents = fc
+	}
+
+	return parser.ParseFile(c.fset, c.File, contents, parser.ParseComments)
+}
+
+// findSelection returns the start and end position of the fields that are
+// suspect to change. It depends on the line, struct or offset selection.
+func (c *Config) findSelection(node ast.Node) (int, int, error) {
+	if c.Line != "" {
+		return c.lineSelection(node)
+	} else if c.Offset != 0 {
+		return c.offsetSelection(node)
+	} else if c.StructName != "" {
+		return c.structSelection(node)
+	} else if c.All {
+		return c.allSelection(node)
+	} else {
+		return 0, 0, errors.New("-line, -offset, -struct or -all is not passed")
+	}
+}
+
+func (c *Config) process(fieldName, tagVal string) (string, error) {
+	var tag string
+	if tagVal != "" {
+		var err error
+		tag, err = strconv.Unquote(tagVal)
+		if err != nil {
+			return "", err
+		}
+	}
+
+	tags, err := structtag.Parse(tag)
+	if err != nil {
+		return "", err
+	}
+
+	tags = c.removeTags(tags)
+	tags, err = c.removeTagOptions(tags)
+	if err != nil {
+		return "", err
+	}
+
+	tags = c.clearTags(tags)
+	tags = c.clearOptions(tags)
+
+	tags, err = c.addTags(fieldName, tags)
+	if err != nil {
+		return "", err
+	}
+
+	tags, err = c.addTagOptions(tags)
+	if err != nil {
+		return "", err
+	}
+
+	if c.Sort {
+		sort.Sort(tags)
+	}
+
+	res := tags.String()
+	if res != "" {
+		res = quote(tags.String())
+	}
+
+	return res, nil
+}
+
+func (c *Config) removeTags(tags *structtag.Tags) *structtag.Tags {
+	if c.Remove == nil || len(c.Remove) == 0 {
+		return tags
+	}
+
+	tags.Delete(c.Remove...)
+	return tags
+}
+
+func (c *Config) clearTags(tags *structtag.Tags) *structtag.Tags {
+	if !c.Clear {
+		return tags
+	}
+
+	tags.Delete(tags.Keys()...)
+	return tags
+}
+
+func (c *Config) clearOptions(tags *structtag.Tags) *structtag.Tags {
+	if !c.ClearOption {
+		return tags
+	}
+
+	for _, t := range tags.Tags() {
+		t.Options = nil
+	}
+
+	return tags
+}
+
+func (c *Config) removeTagOptions(tags *structtag.Tags) (*structtag.Tags, error) {
+	if c.RemoveOptions == nil || len(c.RemoveOptions) == 0 {
+		return tags, nil
+	}
+
+	for _, val := range c.RemoveOptions {
+		// syntax key=option
+		splitted := strings.Split(val, "=")
+		if len(splitted) < 2 {
+			return nil, errors.New("wrong syntax to remove an option. i.e key=option")
+		}
+
+		key := splitted[0]
+		option := strings.Join(splitted[1:], "=")
+
+		tags.DeleteOptions(key, option)
+	}
+
+	return tags, nil
+}
+
+func (c *Config) addTagOptions(tags *structtag.Tags) (*structtag.Tags, error) {
+	if c.AddOptions == nil || len(c.AddOptions) == 0 {
+		return tags, nil
+	}
+
+	for _, val := range c.AddOptions {
+		// syntax key=option
+		splitted := strings.Split(val, "=")
+		if len(splitted) < 2 {
+			return nil, errors.New("wrong syntax to add an option. i.e key=option")
+		}
+
+		key := splitted[0]
+		option := strings.Join(splitted[1:], "=")
+
+		tags.AddOptions(key, option)
+	}
+
+	return tags, nil
+}
+
+func (c *Config) addTags(fieldName string, tags *structtag.Tags) (*structtag.Tags, error) {
+	if c.Add == nil || len(c.Add) == 0 {
+		return tags, nil
+	}
+
+	splitted := camelcase.Split(fieldName)
+	name := ""
+
+	unknown := false
+	switch c.Transform {
+	case "snakecase":
+		var lowerSplitted []string
+		for _, s := range splitted {
+			lowerSplitted = append(lowerSplitted, strings.ToLower(s))
+		}
+
+		name = strings.Join(lowerSplitted, "_")
+	case "lispcase":
+		var lowerSplitted []string
+		for _, s := range splitted {
+			lowerSplitted = append(lowerSplitted, strings.ToLower(s))
+		}
+
+		name = strings.Join(lowerSplitted, "-")
+	case "camelcase":
+		var titled []string
+		for _, s := range splitted {
+			titled = append(titled, strings.Title(s))
+		}
+
+		titled[0] = strings.ToLower(titled[0])
+
+		name = strings.Join(titled, "")
+	case "pascalcase":
+		var titled []string
+		for _, s := range splitted {
+			titled = append(titled, strings.Title(s))
+		}
+
+		name = strings.Join(titled, "")
+	case "titlecase":
+		var titled []string
+		for _, s := range splitted {
+			titled = append(titled, strings.Title(s))
+		}
+
+		name = strings.Join(titled, " ")
+	case "keep":
+		name = fieldName
+	default:
+		unknown = true
+	}
+
+	if c.ValueFormat != "" {
+		prevName := name
+		name = strings.ReplaceAll(c.ValueFormat, "{field}", name)
+		if name == c.ValueFormat {
+			// support old style for backward compatibility
+			name = strings.ReplaceAll(c.ValueFormat, "$field", prevName)
+		}
+	}
+
+	for _, key := range c.Add {
+		splitted = strings.SplitN(key, ":", 2)
+		if len(splitted) >= 2 {
+			key = splitted[0]
+			name = strings.Join(splitted[1:], "")
+		} else if unknown {
+			// the user didn't pass any value but want to use an unknown
+			// transform. We don't return above in the default as the user
+			// might pass a value
+			return nil, fmt.Errorf("unknown transform option %q", c.Transform)
+		}
+
+		tag, err := tags.Get(key)
+		if err != nil {
+			// tag doesn't exist, create a new one
+			tag = &structtag.Tag{
+				Key:  key,
+				Name: name,
+			}
+		} else if c.Override {
+			tag.Name = name
+		}
+
+		if err := tags.Set(tag); err != nil {
+			return nil, err
+		}
+	}
+
+	return tags, nil
+}
+
+// collectStructs collects and maps structType nodes to their positions
+func collectStructs(node ast.Node) map[token.Pos]*structType {
+	structs := make(map[token.Pos]*structType)
+
+	collectStructs := func(n ast.Node) bool {
+		var t ast.Expr
+		var structName string
+
+		switch x := n.(type) {
+		case *ast.TypeSpec:
+			if x.Type == nil {
+				return true
+
+			}
+
+			structName = x.Name.Name
+			t = x.Type
+		case *ast.CompositeLit:
+			t = x.Type
+		case *ast.ValueSpec:
+			structName = x.Names[0].Name
+			t = x.Type
+		case *ast.Field:
+			// this case also catches struct fields and the structName
+			// therefore might contain the field name (which is wrong)
+			// because `x.Type` in this case is not a *ast.StructType.
+			//
+			// We're OK with it, because, in our case *ast.Field represents
+			// a parameter declaration, i.e:
+			//
+			//   func test(arg struct {
+			//   	Field int
+			//   }) {
+			//   }
+			//
+			// and hence the struct name will be `arg`.
+			if len(x.Names) != 0 {
+				structName = x.Names[0].Name
+			}
+			t = x.Type
+		}
+
+		// if expression is in form "*T" or "[]T", dereference to check if "T"
+		// contains a struct expression
+		t = deref(t)
+
+		x, ok := t.(*ast.StructType)
+		if !ok {
+			return true
+		}
+
+		structs[x.Pos()] = &structType{
+			name: structName,
+			node: x,
+		}
+		return true
+	}
+
+	ast.Inspect(node, collectStructs)
+	return structs
+}
+
+func (c *Config) format(file ast.Node, rwErrs error) (string, error) {
+	switch c.Output {
+	case "source":
+		var buf bytes.Buffer
+		err := format.Node(&buf, c.fset, file)
+		if err != nil {
+			return "", err
+		}
+
+		if c.Write {
+			err = ioutil.WriteFile(c.File, buf.Bytes(), 0)
+			if err != nil {
+				return "", err
+			}
+		}
+
+		return buf.String(), nil
+	case "json":
+		// NOTE(arslan): print first the whole file and then cut out our
+		// selection. The reason we don't directly print the struct is that the
+		// printer is not capable of printing loosy comments, comments that are
+		// not part of any field inside a struct. Those are part of *ast.File
+		// and only printed inside a struct if we print the whole file. This
+		// approach is the sanest and simplest way to get a struct printed
+		// back. Second, our cursor might intersect two different structs with
+		// other declarations in between them. Printing the file and cutting
+		// the selection is the easier and simpler to do.
+		var buf bytes.Buffer
+
+		// this is the default config from `format.Node()`, but we add
+		// `printer.SourcePos` to get the original source position of the
+		// modified lines
+		cfg := printer.Config{Mode: printer.SourcePos | printer.UseSpaces | printer.TabIndent, Tabwidth: 8}
+		err := cfg.Fprint(&buf, c.fset, file)
+		if err != nil {
+			return "", err
+		}
+
+		lines, err := parseLines(&buf)
+		if err != nil {
+			return "", err
+		}
+
+		// prevent selection to be larger than the actual number of lines
+		if c.Start > len(lines) || c.End > len(lines) {
+			return "", errors.New("line selection is invalid")
+		}
+
+		out := &output{
+			Start: c.Start,
+			End:   c.End,
+			Lines: lines[c.Start-1 : c.End],
+		}
+
+		if rwErrs != nil {
+			if r, ok := rwErrs.(*rewriteErrors); ok {
+				for _, err := range r.errs {
+					out.Errors = append(out.Errors, err.Error())
+				}
+			}
+		}
+
+		o, err := json.MarshalIndent(out, "", "  ")
+		if err != nil {
+			return "", err
+		}
+
+		return string(o), nil
+	default:
+		return "", fmt.Errorf("unknown output mode: %s", c.Output)
+	}
+}
+
+func (c *Config) lineSelection(file ast.Node) (int, int, error) {
+	var err error
+	splitted := strings.Split(c.Line, ",")
+
+	start, err := strconv.Atoi(splitted[0])
+	if err != nil {
+		return 0, 0, err
+	}
+
+	end := start
+	if len(splitted) == 2 {
+		end, err = strconv.Atoi(splitted[1])
+		if err != nil {
+			return 0, 0, err
+		}
+	}
+
+	if start > end {
+		return 0, 0, errors.New("wrong range. start line cannot be larger than end line")
+	}
+
+	return start, end, nil
+}
+
+func (c *Config) structSelection(file ast.Node) (int, int, error) {
+	structs := collectStructs(file)
+
+	var encStruct *ast.StructType
+	for _, st := range structs {
+		if st.name == c.StructName {
+			encStruct = st.node
+		}
+	}
+
+	if encStruct == nil {
+		return 0, 0, errors.New("struct name does not exist")
+	}
+
+	// if field name has been specified as well, only select the given field
+	if c.FieldName != "" {
+		return c.fieldSelection(encStruct)
+	}
+
+	start := c.fset.Position(encStruct.Pos()).Line
+	end := c.fset.Position(encStruct.End()).Line
+
+	return start, end, nil
+}
+
+func (c *Config) fieldSelection(st *ast.StructType) (int, int, error) {
+	var encField *ast.Field
+	for _, f := range st.Fields.List {
+		for _, field := range f.Names {
+			if field.Name == c.FieldName {
+				encField = f
+			}
+		}
+	}
+
+	if encField == nil {
+		return 0, 0, fmt.Errorf("struct %q doesn't have field name %q", c.StructName, c.FieldName)
+	}
+
+	start := c.fset.Position(encField.Pos()).Line
+	end := c.fset.Position(encField.End()).Line
+
+	return start, end, nil
+}
+
+func (c *Config) offsetSelection(file ast.Node) (int, int, error) {
+	structs := collectStructs(file)
+
+	var encStruct *ast.StructType
+	for _, st := range structs {
+		structBegin := c.fset.Position(st.node.Pos()).Offset
+		structEnd := c.fset.Position(st.node.End()).Offset
+
+		if structBegin <= c.Offset && c.Offset <= structEnd {
+			encStruct = st.node
+			break
+		}
+	}
+
+	if encStruct == nil {
+		return 0, 0, errors.New("offset is not inside a struct")
+	}
+
+	// offset selects all fields
+	start := c.fset.Position(encStruct.Pos()).Line
+	end := c.fset.Position(encStruct.End()).Line
+
+	return start, end, nil
+}
+
+// allSelection selects all structs inside a file
+func (c *Config) allSelection(file ast.Node) (int, int, error) {
+	start := 1
+	end := c.fset.File(file.Pos()).LineCount()
+
+	return start, end, nil
+}
+
+func isPublicName(name string) bool {
+	for _, c := range name {
+		return unicode.IsUpper(c)
+	}
+	return false
+}
+
+// rewrite rewrites the node for structs between the start and end
+// positions
+func (c *Config) rewrite(node ast.Node, start, end int) (ast.Node, error) {
+	errs := &rewriteErrors{errs: make([]error, 0)}
+
+	rewriteFunc := func(n ast.Node) bool {
+		x, ok := n.(*ast.StructType)
+		if !ok {
+			return true
+		}
+
+		for _, f := range x.Fields.List {
+			line := c.fset.Position(f.Pos()).Line
+
+			if !(start <= line && line <= end) {
+				continue
+			}
+
+			fieldName := ""
+			if len(f.Names) != 0 {
+				for _, field := range f.Names {
+					if !c.SkipUnexportedFields || isPublicName(field.Name) {
+						fieldName = field.Name
+						break
+					}
+				}
+			}
+
+			// anonymous field
+			if f.Names == nil {
+				ident, ok := f.Type.(*ast.Ident)
+				if !ok {
+					continue
+				}
+
+				if !c.SkipUnexportedFields {
+					fieldName = ident.Name
+				}
+			}
+
+			// nothing to process, continue with next line
+			if fieldName == "" {
+				continue
+			}
+
+			if f.Tag == nil {
+				f.Tag = &ast.BasicLit{}
+			}
+
+			res, err := c.process(fieldName, f.Tag.Value)
+			if err != nil {
+				errs.Append(fmt.Errorf("%s:%d:%d:%s",
+					c.fset.Position(f.Pos()).Filename,
+					c.fset.Position(f.Pos()).Line,
+					c.fset.Position(f.Pos()).Column,
+					err))
+				continue
+			}
+
+			f.Tag.Value = res
+		}
+
+		return true
+	}
+
+	ast.Inspect(node, rewriteFunc)
+
+	c.Start = start
+	c.End = end
+
+	if len(errs.errs) == 0 {
+		return node, nil
+	}
+
+	return node, errs
+}
+
+// validate validates whether the config is valid or not
+func (c *Config) validate() error {
+	if c.File == "" {
+		return errors.New("no file is passed")
+	}
+
+	if c.Line == "" && c.Offset == 0 && c.StructName == "" && !c.All {
+		return errors.New("-line, -offset, -struct or -all is not passed")
+	}
+
+	if c.Line != "" && c.Offset != 0 ||
+		c.Line != "" && c.StructName != "" ||
+		c.Offset != 0 && c.StructName != "" {
+		return errors.New("-line, -offset or -struct cannot be used together. pick one")
+	}
+
+	if (c.Add == nil || len(c.Add) == 0) &&
+		(c.AddOptions == nil || len(c.AddOptions) == 0) &&
+		!c.Clear &&
+		!c.ClearOption &&
+		(c.RemoveOptions == nil || len(c.RemoveOptions) == 0) &&
+		(c.Remove == nil || len(c.Remove) == 0) {
+		return errors.New("one of " +
+			"[-add-tags, -add-options, -remove-tags, -remove-options, -clear-tags, -clear-options]" +
+			" should be defined")
+	}
+
+	if c.FieldName != "" && c.StructName == "" {
+		return errors.New("-field is requiring -struct")
+	}
+
+	return nil
+}
+
+func quote(tag string) string {
+	return "`" + tag + "`"
+}
+
+type rewriteErrors struct {
+	errs []error
+}
+
+func (r *rewriteErrors) Error() string {
+	var buf bytes.Buffer
+	for _, e := range r.errs {
+		buf.WriteString(fmt.Sprintf("%s\n", e.Error()))
+	}
+	return buf.String()
+}
+
+func (r *rewriteErrors) Append(err error) {
+	if err == nil {
+		return
+	}
+
+	r.errs = append(r.errs, err)
+}
+
+// parseLines parses the given buffer and returns a slice of lines
+func parseLines(buf io.Reader) ([]string, error) {
+	var lines []string
+	scanner := bufio.NewScanner(buf)
+	for scanner.Scan() {
+		txt := scanner.Text()
+
+		// check for any line directive and store it for next iteration to
+		// re-construct the original file. If it's not a line directive,
+		// continue consturcting the original file
+		if !strings.HasPrefix(txt, "//line") {
+			lines = append(lines, txt)
+			continue
+		}
+
+		lineNr, err := split(txt)
+		if err != nil {
+			return nil, err
+		}
+
+		for i := len(lines); i < lineNr-1; i++ {
+			lines = append(lines, "")
+		}
+
+		lines = lines[:lineNr-1]
+	}
+
+	if err := scanner.Err(); err != nil {
+		return nil, fmt.Errorf("invalid scanner inputl: %s", err)
+	}
+
+	return lines, nil
+}
+
+// split splits the given line directive and returns the line number
+// see https://golang.org/cmd/compile/#hdr-Compiler_Directives for more
+// information
+// NOTE(arslan): this only splits the line directive that the go.Parser
+// outputs. If the go parser changes the format of the line directive, make
+// sure to fix it in the below function
+func split(line string) (int, error) {
+	for i := len(line) - 1; i >= 0; i-- {
+		if line[i] != ':' {
+			continue
+		}
+
+		nr, err := strconv.Atoi(line[i+1:])
+		if err != nil {
+			return 0, err
+		}
+
+		return nr, nil
+	}
+
+	return 0, fmt.Errorf("couldn't parse line: '%s'", line)
+}
+
+// deref takes an expression, and removes all its leading "*" and "[]"
+// operator. Uuse case : if found expression is a "*t" or "[]t", we need to
+// check if "t" contains a struct expression.
+func deref(x ast.Expr) ast.Expr {
+	switch t := x.(type) {
+	case *ast.StarExpr:
+		return deref(t.X)
+	case *ast.ArrayType:
+		return deref(t.Elt)
+	}
+	return x
+}
diff --git a/internal/gomodifytags/gomodifytags_test.go b/internal/gomodifytags/gomodifytags_test.go
new file mode 100644
index 0000000..000bce1
--- /dev/null
+++ b/internal/gomodifytags/gomodifytags_test.go
@@ -0,0 +1,929 @@
+package gomodifytags
+
+import (
+	"bytes"
+	"errors"
+	"flag"
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"reflect"
+	"strings"
+	"testing"
+)
+
+var update = flag.Bool("update", false, "update golden (.out) files")
+
+// This is the directory where our test fixtures are.
+const fixtureDir = "./test-fixtures"
+
+func TestRewrite(t *testing.T) {
+	test := []struct {
+		cfg  *Config
+		file string
+	}{
+		{
+			file: "struct_add",
+			cfg: &Config{
+				Add:        []string{"json"},
+				Output:     "source",
+				StructName: "foo",
+				Transform:  "snakecase",
+			},
+		},
+		{
+			file: "struct_add_existing",
+			cfg: &Config{
+				Add:        []string{"json"},
+				Output:     "source",
+				StructName: "foo",
+				Transform:  "snakecase",
+			},
+		},
+		{
+			file: "struct_format",
+			cfg: &Config{
+				Add:         []string{"gaum"},
+				Output:      "source",
+				StructName:  "foo",
+				Transform:   "snakecase",
+				ValueFormat: "field_name={field}",
+			},
+		},
+		{
+			file: "struct_format_existing",
+			cfg: &Config{
+				Add:         []string{"gaum"},
+				Output:      "source",
+				StructName:  "foo",
+				Transform:   "snakecase",
+				ValueFormat: "field_name={field}",
+			},
+		},
+		{
+			file: "struct_format_oldstyle",
+			cfg: &Config{
+				Add:         []string{"gaum"},
+				Output:      "source",
+				StructName:  "foo",
+				Transform:   "snakecase",
+				ValueFormat: "field_name=$field",
+			},
+		},
+		{
+			file: "struct_format_existing_oldstyle",
+			cfg: &Config{
+				Add:         []string{"gaum"},
+				Output:      "source",
+				StructName:  "foo",
+				Transform:   "snakecase",
+				ValueFormat: "field_name=$field",
+			},
+		},
+		{
+			file: "struct_remove",
+			cfg: &Config{
+				Remove:     []string{"json"},
+				Output:     "source",
+				StructName: "foo",
+			},
+		},
+		{
+			file: "struct_clear_tags",
+			cfg: &Config{
+				Clear:      true,
+				Output:     "source",
+				StructName: "foo",
+			},
+		},
+		{
+			file: "struct_clear_options",
+			cfg: &Config{
+				ClearOption: true,
+				Output:      "source",
+				StructName:  "foo",
+			},
+		},
+		{
+			file: "line_add",
+			cfg: &Config{
+				Add:       []string{"json"},
+				Output:    "source",
+				Line:      "4",
+				Transform: "snakecase",
+			},
+		},
+		{
+			file: "line_add_override",
+			cfg: &Config{
+				Add:       []string{"json"},
+				Output:    "source",
+				Line:      "4,5",
+				Transform: "snakecase",
+				Override:  true,
+			},
+		},
+		{
+			file: "line_add_override_column",
+			cfg: &Config{
+				Add:       []string{"json:MyBar:bar"},
+				Output:    "source",
+				Line:      "4,4",
+				Transform: "snakecase",
+				Override:  true,
+			},
+		},
+		{
+			file: "line_add_override_mixed_column_and_equal",
+			cfg: &Config{
+				Add:       []string{"json:MyBar:bar:foo=qux"},
+				Output:    "source",
+				Line:      "4,4",
+				Transform: "snakecase",
+				Override:  true,
+			},
+		},
+		{
+			file: "line_add_override_multi_equal",
+			cfg: &Config{
+				Add:       []string{"json:MyBar=bar=foo"},
+				Output:    "source",
+				Line:      "4,4",
+				Transform: "snakecase",
+				Override:  true,
+			},
+		},
+		{
+			file: "line_add_override_multi_column",
+			cfg: &Config{
+				Add:       []string{"json:MyBar:bar:foo"},
+				Output:    "source",
+				Line:      "4,4",
+				Transform: "snakecase",
+				Override:  true,
+			},
+		},
+		{
+			file: "line_add_no_override",
+			cfg: &Config{
+				Add:       []string{"json"},
+				Output:    "source",
+				Line:      "4,5",
+				Transform: "snakecase",
+			},
+		},
+		{
+			file: "line_add_outside",
+			cfg: &Config{
+				Add:       []string{"json"},
+				Output:    "source",
+				Line:      "2,8",
+				Transform: "snakecase",
+			},
+		},
+		{
+			file: "line_add_outside_partial_start",
+			cfg: &Config{
+				Add:       []string{"json"},
+				Output:    "source",
+				Line:      "2,5",
+				Transform: "snakecase",
+			},
+		},
+		{
+			file: "line_add_outside_partial_end",
+			cfg: &Config{
+				Add:       []string{"json"},
+				Output:    "source",
+				Line:      "5,8",
+				Transform: "snakecase",
+			},
+		},
+		{
+			file: "line_add_intersect_partial",
+			cfg: &Config{
+				Add:       []string{"json"},
+				Output:    "source",
+				Line:      "5,11",
+				Transform: "snakecase",
+			},
+		},
+		{
+			file: "line_add_comment",
+			cfg: &Config{
+				Add:       []string{"json"},
+				Output:    "source",
+				Line:      "6,7",
+				Transform: "snakecase",
+			},
+		},
+		{
+			file: "line_add_option",
+			cfg: &Config{
+				AddOptions: []string{"json=omitempty"},
+				Output:     "source",
+				Line:       "4,7",
+			},
+		},
+		{
+			file: "line_add_option_existing",
+			cfg: &Config{
+				AddOptions: []string{"json=omitempty"},
+				Output:     "source",
+				Line:       "6,8",
+			},
+		},
+		{
+			file: "line_add_multiple_option",
+			cfg: &Config{
+				AddOptions: []string{"json=omitempty", "hcl=squash"},
+				Add:        []string{"hcl"},
+				Output:     "source",
+				Line:       "4,7",
+				Transform:  "snakecase",
+			},
+		},
+		{
+			file: "line_add_option_with_equal",
+			cfg: &Config{
+				AddOptions: []string{"validate=max=32"},
+				Add:        []string{"validate"},
+				Output:     "source",
+				Line:       "4,7",
+				Transform:  "snakecase",
+			},
+		},
+		{
+			file: "line_remove",
+			cfg: &Config{
+				Remove: []string{"json"},
+				Output: "source",
+				Line:   "5,7",
+			},
+		},
+		{
+			file: "line_remove_option",
+			cfg: &Config{
+				RemoveOptions: []string{"hcl=squash"},
+				Output:        "source",
+				Line:          "4,8",
+			},
+		},
+		{
+			file: "line_remove_options",
+			cfg: &Config{
+				RemoveOptions: []string{"json=omitempty", "hcl=omitnested"},
+				Output:        "source",
+				Line:          "4,7",
+			},
+		},
+		{
+			file: "line_remove_option_with_equal",
+			cfg: &Config{
+				RemoveOptions: []string{"validate=max=32"},
+				Output:        "source",
+				Line:          "4,7",
+			},
+		},
+		{
+			file: "line_multiple_add",
+			cfg: &Config{
+				Add:       []string{"json"},
+				Output:    "source",
+				Line:      "5,6",
+				Transform: "camelcase",
+			},
+		},
+		{
+			file: "line_lispcase_add",
+			cfg: &Config{
+				Add:       []string{"json"},
+				Output:    "source",
+				Line:      "4,6",
+				Transform: "lispcase",
+			},
+		},
+		{
+			file: "line_camelcase_add",
+			cfg: &Config{
+				Add:       []string{"json"},
+				Output:    "source",
+				Line:      "4,5",
+				Transform: "camelcase",
+			},
+		},
+		{
+			file: "line_camelcase_add_embedded",
+			cfg: &Config{
+				Add:       []string{"json"},
+				Output:    "source",
+				Line:      "4,6",
+				Transform: "camelcase",
+			},
+		},
+		{
+			file: "line_value_add",
+			cfg: &Config{
+				Add:    []string{"json:foo"},
+				Output: "source",
+				Line:   "4,6",
+			},
+		},
+		{
+			file: "offset_add",
+			cfg: &Config{
+				Add:       []string{"json"},
+				Output:    "source",
+				Offset:    32,
+				Transform: "snakecase",
+			},
+		},
+		{
+			file: "offset_add_composite",
+			cfg: &Config{
+				Add:       []string{"json"},
+				Output:    "source",
+				Offset:    40,
+				Transform: "snakecase",
+			},
+		},
+		{
+			file: "offset_add_duplicate",
+			cfg: &Config{
+				Add:       []string{"json"},
+				Output:    "source",
+				Offset:    209,
+				Transform: "snakecase",
+			},
+		},
+		{
+			file: "offset_add_literal_in",
+			cfg: &Config{
+				Add:       []string{"json"},
+				Output:    "source",
+				Offset:    46,
+				Transform: "snakecase",
+			},
+		},
+		{
+			file: "offset_add_literal_out",
+			cfg: &Config{
+				Add:       []string{"json"},
+				Output:    "source",
+				Offset:    32,
+				Transform: "snakecase",
+			},
+		},
+		{
+			file: "errors",
+			cfg: &Config{
+				Add:       []string{"json"},
+				Output:    "source",
+				Line:      "4,7",
+				Transform: "snakecase",
+			},
+		},
+		{
+			file: "line_pascalcase_add",
+			cfg: &Config{
+				Add:       []string{"json"},
+				Output:    "source",
+				Line:      "4,5",
+				Transform: "pascalcase",
+			},
+		},
+		{
+			file: "line_pascalcase_add_embedded",
+			cfg: &Config{
+				Add:       []string{"json"},
+				Output:    "source",
+				Line:      "4,6",
+				Transform: "pascalcase",
+			},
+		},
+		{
+			file: "not_formatted",
+			cfg: &Config{
+				Add:       []string{"json"},
+				Output:    "source",
+				Line:      "3,4",
+				Transform: "snakecase",
+			},
+		},
+		{
+			file: "skip_private",
+			cfg: &Config{
+				Add:                  []string{"json"},
+				Output:               "source",
+				StructName:           "foo",
+				Transform:            "snakecase",
+				SkipUnexportedFields: true,
+			},
+		},
+		{
+			file: "skip_private_multiple_names",
+			cfg: &Config{
+				Add:                  []string{"json"},
+				Output:               "source",
+				StructName:           "foo",
+				Transform:            "snakecase",
+				SkipUnexportedFields: true,
+			},
+		},
+		{
+			file: "skip_embedded",
+			cfg: &Config{
+				Add:                  []string{"json"},
+				Output:               "source",
+				StructName:           "StationCreated",
+				Transform:            "snakecase",
+				SkipUnexportedFields: true,
+			},
+		},
+		{
+			file: "all_structs",
+			cfg: &Config{
+				Add:       []string{"json"},
+				Output:    "source",
+				All:       true,
+				Transform: "snakecase",
+			},
+		},
+		{
+			file: "line_titlecase_add",
+			cfg: &Config{
+				Add:       []string{"json"},
+				Output:    "source",
+				Line:      "4,6",
+				Transform: "titlecase",
+			},
+		},
+		{
+			file: "line_titlecase_add_embedded",
+			cfg: &Config{
+				Add:       []string{"json"},
+				Output:    "source",
+				Line:      "4,6",
+				Transform: "titlecase",
+			},
+		},
+		{
+			file: "field_add",
+			cfg: &Config{
+				Add:        []string{"json"},
+				Output:     "source",
+				StructName: "foo",
+				FieldName:  "bar",
+				Transform:  "snakecase",
+			},
+		},
+		{
+			file: "field_add_same_line",
+			cfg: &Config{
+				Add:        []string{"json"},
+				Output:     "source",
+				StructName: "foo",
+				FieldName:  "qux",
+				Transform:  "snakecase",
+			},
+		},
+		{
+			file: "field_add_existing",
+			cfg: &Config{
+				Add:        []string{"json"},
+				Output:     "source",
+				StructName: "foo",
+				FieldName:  "bar",
+				Transform:  "snakecase",
+			},
+		},
+		{
+			file: "field_clear_tags",
+			cfg: &Config{
+				Clear:      true,
+				Output:     "source",
+				StructName: "foo",
+				FieldName:  "bar",
+			},
+		},
+		{
+			file: "field_clear_options",
+			cfg: &Config{
+				ClearOption: true,
+				Output:      "source",
+				StructName:  "foo",
+				FieldName:   "bar",
+			},
+		},
+		{
+			file: "field_remove",
+			cfg: &Config{
+				Remove:     []string{"json"},
+				Output:     "source",
+				StructName: "foo",
+				FieldName:  "bar",
+			},
+		},
+		{
+			file: "offset_anonymous_struct",
+			cfg: &Config{
+				Add:       []string{"json"},
+				Output:    "source",
+				Offset:    45,
+				Transform: "camelcase",
+			},
+		},
+		{
+			file: "offset_star_struct",
+			cfg: &Config{
+				Add:       []string{"json"},
+				Output:    "source",
+				Offset:    35,
+				Transform: "camelcase",
+			},
+		},
+		{
+			file: "offset_array_struct",
+			cfg: &Config{
+				Add:       []string{"json"},
+				Output:    "source",
+				Offset:    35,
+				Transform: "camelcase",
+			},
+		},
+	}
+
+	for _, ts := range test {
+		t.Run(ts.file, func(t *testing.T) {
+			ts.cfg.File = filepath.Join(fixtureDir, fmt.Sprintf("%s.input", ts.file))
+
+			node, err := ts.cfg.parse()
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			start, end, err := ts.cfg.findSelection(node)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			rewrittenNode, err := ts.cfg.rewrite(node, start, end)
+			if err != nil {
+				if _, ok := err.(*rewriteErrors); !ok {
+					t.Fatal(err)
+				}
+			}
+
+			out, err := ts.cfg.format(rewrittenNode, err)
+			if err != nil {
+				t.Fatal(err)
+			}
+			got := []byte(out)
+
+			// update golden file if necessary
+			golden := filepath.Join(fixtureDir, fmt.Sprintf("%s.golden", ts.file))
+			if *update {
+				err := ioutil.WriteFile(golden, got, 0644)
+				if err != nil {
+					t.Error(err)
+				}
+				return
+			}
+
+			// get golden file
+			want, err := ioutil.ReadFile(golden)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			var from []byte
+			if ts.cfg.Modified != nil {
+				from, err = ioutil.ReadAll(ts.cfg.Modified)
+			} else {
+				from, err = ioutil.ReadFile(ts.cfg.File)
+			}
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			// compare
+			if !bytes.Equal(got, want) {
+				t.Errorf("case %s\ngot:\n====\n\n%s\nwant:\n=====\n\n%s\nfrom:\n=====\n\n%s\n",
+					ts.file, got, want, from)
+			}
+		})
+	}
+}
+
+func TestJSON(t *testing.T) {
+	test := []struct {
+		cfg  *Config
+		file string
+		err  error
+	}{
+		{
+			file: "json_single",
+			cfg: &Config{
+				Add:  []string{"json"},
+				Line: "5",
+			},
+		},
+		{
+			file: "json_full",
+			cfg: &Config{
+				Add:  []string{"json"},
+				Line: "4,6",
+			},
+		},
+		{
+			file: "json_intersection",
+			cfg: &Config{
+				Add:  []string{"json"},
+				Line: "5,16",
+			},
+		},
+		{
+			// both small & end range larger than file
+			file: "json_single",
+			cfg: &Config{
+				Add:  []string{"json"},
+				Line: "30,32", // invalid selection
+			},
+			err: errors.New("line selection is invalid"),
+		},
+		{
+			// end range larger than file
+			file: "json_single",
+			cfg: &Config{
+				Add:  []string{"json"},
+				Line: "4,50", // invalid selection
+			},
+			err: errors.New("line selection is invalid"),
+		},
+		{
+			file: "json_errors",
+			cfg: &Config{
+				Add:  []string{"json"},
+				Line: "4,7",
+			},
+		},
+		{
+			file: "json_not_formatted",
+			cfg: &Config{
+				Add:  []string{"json"},
+				Line: "3,4",
+			},
+		},
+		{
+			file: "json_not_formatted_2",
+			cfg: &Config{
+				Add:  []string{"json"},
+				Line: "3,3",
+			},
+		},
+		{
+			file: "json_not_formatted_3",
+			cfg: &Config{
+				Add:    []string{"json"},
+				Offset: 23,
+			},
+		},
+		{
+			file: "json_not_formatted_4",
+			cfg: &Config{
+				Add:    []string{"json"},
+				Offset: 51,
+			},
+		},
+		{
+			file: "json_not_formatted_5",
+			cfg: &Config{
+				Add:    []string{"json"},
+				Offset: 29,
+			},
+		},
+		{
+			file: "json_not_formatted_6",
+			cfg: &Config{
+				Add:  []string{"json"},
+				Line: "2,54",
+			},
+		},
+		{
+			file: "json_all_structs",
+			cfg: &Config{
+				Add: []string{"json"},
+				All: true,
+			},
+		},
+	}
+
+	for _, ts := range test {
+		t.Run(ts.file, func(t *testing.T) {
+			ts.cfg.File = filepath.Join(fixtureDir, fmt.Sprintf("%s.input", ts.file))
+			// these are explicit and shouldn't be changed for this particular
+			// main test
+			ts.cfg.Output = "json"
+			ts.cfg.Transform = "camelcase"
+
+			node, err := ts.cfg.parse()
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			start, end, err := ts.cfg.findSelection(node)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			rewrittenNode, err := ts.cfg.rewrite(node, start, end)
+			if err != nil {
+				if _, ok := err.(*rewriteErrors); !ok {
+					t.Fatal(err)
+				}
+			}
+
+			out, err := ts.cfg.format(rewrittenNode, err)
+			if !reflect.DeepEqual(err, ts.err) {
+				t.Logf("want: %v", ts.err)
+				t.Logf("got: %v", err)
+				t.Fatalf("unexpected error")
+			}
+
+			if ts.err != nil {
+				return
+			}
+
+			got := []byte(out)
+
+			// update golden file if necessary
+			golden := filepath.Join(fixtureDir, fmt.Sprintf("%s.golden", ts.file))
+			if *update {
+				err := ioutil.WriteFile(golden, got, 0644)
+				if err != nil {
+					t.Error(err)
+				}
+				return
+			}
+
+			// get golden file
+			want, err := ioutil.ReadFile(golden)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			from, err := ioutil.ReadFile(ts.cfg.File)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			// compare
+			if !bytes.Equal(got, want) {
+				t.Errorf("case %s\ngot:\n====\n\n%s\nwant:\n=====\n\n%s\nfrom:\n=====\n\n%s\n",
+					ts.file, got, want, from)
+			}
+		})
+	}
+}
+
+func TestModifiedRewrite(t *testing.T) {
+	cfg := &Config{
+		Add:        []string{"json"},
+		Output:     "source",
+		StructName: "foo",
+		Transform:  "snakecase",
+		File:       "struct_add_modified",
+		Modified: strings.NewReader(`struct_add_modified
+55
+package foo
+
+type foo struct {
+	bar string
+	t   bool
+}
+`),
+	}
+
+	node, err := cfg.parse()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	start, end, err := cfg.findSelection(node)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	rewrittenNode, err := cfg.rewrite(node, start, end)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	got, err := cfg.format(rewrittenNode, err)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	golden := filepath.Join(fixtureDir, "struct_add.golden")
+	want, err := ioutil.ReadFile(golden)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// compare
+	if !bytes.Equal([]byte(got), want) {
+		t.Errorf("got:\n====\n%s\nwant:\n====\n%s\n", got, want)
+	}
+}
+
+func TestModifiedFileMissing(t *testing.T) {
+	cfg := &Config{
+		Add:        []string{"json"},
+		Output:     "source",
+		StructName: "foo",
+		Transform:  "snakecase",
+		File:       "struct_add_modified",
+		Modified: strings.NewReader(`file_that_doesnt_exist
+55
+package foo
+
+type foo struct {
+	bar string
+	t   bool
+}
+`),
+	}
+
+	_, err := cfg.parse()
+	if err == nil {
+		t.Fatal("expected error")
+	}
+}
+
+func TestParseLines(t *testing.T) {
+	var tests = []struct {
+		file string
+	}{
+		{file: "line_directive_unix"},
+		{file: "line_directive_windows"},
+	}
+
+	for _, ts := range tests {
+		ts := ts
+
+		t.Run(ts.file, func(t *testing.T) {
+			filePath := filepath.Join(fixtureDir, fmt.Sprintf("%s.input", ts.file))
+
+			file, err := os.Open(filePath)
+			if err != nil {
+				t.Fatal(err)
+			}
+			defer file.Close()
+
+			out, err := parseLines(file)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			toBytes := func(lines []string) []byte {
+				var buf bytes.Buffer
+				for _, line := range lines {
+					buf.WriteString(line + "\n")
+				}
+				return buf.Bytes()
+			}
+
+			got := toBytes(out)
+
+			// update golden file if necessary
+			golden := filepath.Join(fixtureDir, fmt.Sprintf("%s.golden", ts.file))
+
+			if *update {
+				err := ioutil.WriteFile(golden, got, 0644)
+				if err != nil {
+					t.Error(err)
+				}
+				return
+			}
+
+			// get golden file
+			want, err := ioutil.ReadFile(golden)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			from, err := ioutil.ReadFile(filePath)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			// compare
+			if !bytes.Equal(got, want) {
+				t.Errorf("case %s\ngot:\n====\n\n%s\nwant:\n=====\n\n%s\nfrom:\n=====\n\n%s\n",
+					ts.file, got, want, from)
+			}
+
+		})
+	}
+}
diff --git a/test-fixtures/all_structs.golden b/internal/gomodifytags/test-fixtures/all_structs.golden
similarity index 100%
rename from test-fixtures/all_structs.golden
rename to internal/gomodifytags/test-fixtures/all_structs.golden
diff --git a/test-fixtures/all_structs.input b/internal/gomodifytags/test-fixtures/all_structs.input
similarity index 100%
rename from test-fixtures/all_structs.input
rename to internal/gomodifytags/test-fixtures/all_structs.input
diff --git a/test-fixtures/errors.golden b/internal/gomodifytags/test-fixtures/errors.golden
similarity index 100%
rename from test-fixtures/errors.golden
rename to internal/gomodifytags/test-fixtures/errors.golden
diff --git a/test-fixtures/errors.input b/internal/gomodifytags/test-fixtures/errors.input
similarity index 100%
rename from test-fixtures/errors.input
rename to internal/gomodifytags/test-fixtures/errors.input
diff --git a/test-fixtures/field_add.golden b/internal/gomodifytags/test-fixtures/field_add.golden
similarity index 100%
rename from test-fixtures/field_add.golden
rename to internal/gomodifytags/test-fixtures/field_add.golden
diff --git a/test-fixtures/field_add.input b/internal/gomodifytags/test-fixtures/field_add.input
similarity index 100%
rename from test-fixtures/field_add.input
rename to internal/gomodifytags/test-fixtures/field_add.input
diff --git a/test-fixtures/field_add_existing.golden b/internal/gomodifytags/test-fixtures/field_add_existing.golden
similarity index 100%
rename from test-fixtures/field_add_existing.golden
rename to internal/gomodifytags/test-fixtures/field_add_existing.golden
diff --git a/test-fixtures/field_add_existing.input b/internal/gomodifytags/test-fixtures/field_add_existing.input
similarity index 100%
rename from test-fixtures/field_add_existing.input
rename to internal/gomodifytags/test-fixtures/field_add_existing.input
diff --git a/test-fixtures/field_add_same_line.golden b/internal/gomodifytags/test-fixtures/field_add_same_line.golden
similarity index 100%
rename from test-fixtures/field_add_same_line.golden
rename to internal/gomodifytags/test-fixtures/field_add_same_line.golden
diff --git a/test-fixtures/field_add_same_line.input b/internal/gomodifytags/test-fixtures/field_add_same_line.input
similarity index 100%
rename from test-fixtures/field_add_same_line.input
rename to internal/gomodifytags/test-fixtures/field_add_same_line.input
diff --git a/test-fixtures/field_clear_options.golden b/internal/gomodifytags/test-fixtures/field_clear_options.golden
similarity index 100%
rename from test-fixtures/field_clear_options.golden
rename to internal/gomodifytags/test-fixtures/field_clear_options.golden
diff --git a/test-fixtures/field_clear_options.input b/internal/gomodifytags/test-fixtures/field_clear_options.input
similarity index 100%
rename from test-fixtures/field_clear_options.input
rename to internal/gomodifytags/test-fixtures/field_clear_options.input
diff --git a/test-fixtures/field_clear_tags.golden b/internal/gomodifytags/test-fixtures/field_clear_tags.golden
similarity index 100%
rename from test-fixtures/field_clear_tags.golden
rename to internal/gomodifytags/test-fixtures/field_clear_tags.golden
diff --git a/test-fixtures/field_clear_tags.input b/internal/gomodifytags/test-fixtures/field_clear_tags.input
similarity index 100%
rename from test-fixtures/field_clear_tags.input
rename to internal/gomodifytags/test-fixtures/field_clear_tags.input
diff --git a/test-fixtures/field_remove.golden b/internal/gomodifytags/test-fixtures/field_remove.golden
similarity index 100%
rename from test-fixtures/field_remove.golden
rename to internal/gomodifytags/test-fixtures/field_remove.golden
diff --git a/test-fixtures/field_remove.input b/internal/gomodifytags/test-fixtures/field_remove.input
similarity index 100%
rename from test-fixtures/field_remove.input
rename to internal/gomodifytags/test-fixtures/field_remove.input
diff --git a/test-fixtures/json_all_structs.golden b/internal/gomodifytags/test-fixtures/json_all_structs.golden
similarity index 100%
rename from test-fixtures/json_all_structs.golden
rename to internal/gomodifytags/test-fixtures/json_all_structs.golden
diff --git a/test-fixtures/json_all_structs.input b/internal/gomodifytags/test-fixtures/json_all_structs.input
similarity index 100%
rename from test-fixtures/json_all_structs.input
rename to internal/gomodifytags/test-fixtures/json_all_structs.input
diff --git a/test-fixtures/json_errors.golden b/internal/gomodifytags/test-fixtures/json_errors.golden
similarity index 100%
rename from test-fixtures/json_errors.golden
rename to internal/gomodifytags/test-fixtures/json_errors.golden
diff --git a/test-fixtures/json_errors.input b/internal/gomodifytags/test-fixtures/json_errors.input
similarity index 100%
rename from test-fixtures/json_errors.input
rename to internal/gomodifytags/test-fixtures/json_errors.input
diff --git a/test-fixtures/json_full.golden b/internal/gomodifytags/test-fixtures/json_full.golden
similarity index 100%
rename from test-fixtures/json_full.golden
rename to internal/gomodifytags/test-fixtures/json_full.golden
diff --git a/test-fixtures/json_full.input b/internal/gomodifytags/test-fixtures/json_full.input
similarity index 100%
rename from test-fixtures/json_full.input
rename to internal/gomodifytags/test-fixtures/json_full.input
diff --git a/test-fixtures/json_intersection.golden b/internal/gomodifytags/test-fixtures/json_intersection.golden
similarity index 100%
rename from test-fixtures/json_intersection.golden
rename to internal/gomodifytags/test-fixtures/json_intersection.golden
diff --git a/test-fixtures/json_intersection.input b/internal/gomodifytags/test-fixtures/json_intersection.input
similarity index 100%
rename from test-fixtures/json_intersection.input
rename to internal/gomodifytags/test-fixtures/json_intersection.input
diff --git a/test-fixtures/json_not_formatted.golden b/internal/gomodifytags/test-fixtures/json_not_formatted.golden
similarity index 100%
rename from test-fixtures/json_not_formatted.golden
rename to internal/gomodifytags/test-fixtures/json_not_formatted.golden
diff --git a/test-fixtures/json_not_formatted.input b/internal/gomodifytags/test-fixtures/json_not_formatted.input
similarity index 100%
rename from test-fixtures/json_not_formatted.input
rename to internal/gomodifytags/test-fixtures/json_not_formatted.input
diff --git a/test-fixtures/json_not_formatted_2.golden b/internal/gomodifytags/test-fixtures/json_not_formatted_2.golden
similarity index 100%
rename from test-fixtures/json_not_formatted_2.golden
rename to internal/gomodifytags/test-fixtures/json_not_formatted_2.golden
diff --git a/test-fixtures/json_not_formatted_2.input b/internal/gomodifytags/test-fixtures/json_not_formatted_2.input
similarity index 100%
rename from test-fixtures/json_not_formatted_2.input
rename to internal/gomodifytags/test-fixtures/json_not_formatted_2.input
diff --git a/test-fixtures/json_not_formatted_3.golden b/internal/gomodifytags/test-fixtures/json_not_formatted_3.golden
similarity index 100%
rename from test-fixtures/json_not_formatted_3.golden
rename to internal/gomodifytags/test-fixtures/json_not_formatted_3.golden
diff --git a/test-fixtures/json_not_formatted_3.input b/internal/gomodifytags/test-fixtures/json_not_formatted_3.input
similarity index 100%
rename from test-fixtures/json_not_formatted_3.input
rename to internal/gomodifytags/test-fixtures/json_not_formatted_3.input
diff --git a/test-fixtures/json_not_formatted_4.golden b/internal/gomodifytags/test-fixtures/json_not_formatted_4.golden
similarity index 100%
rename from test-fixtures/json_not_formatted_4.golden
rename to internal/gomodifytags/test-fixtures/json_not_formatted_4.golden
diff --git a/test-fixtures/json_not_formatted_4.input b/internal/gomodifytags/test-fixtures/json_not_formatted_4.input
similarity index 100%
rename from test-fixtures/json_not_formatted_4.input
rename to internal/gomodifytags/test-fixtures/json_not_formatted_4.input
diff --git a/test-fixtures/json_not_formatted_5.golden b/internal/gomodifytags/test-fixtures/json_not_formatted_5.golden
similarity index 100%
rename from test-fixtures/json_not_formatted_5.golden
rename to internal/gomodifytags/test-fixtures/json_not_formatted_5.golden
diff --git a/test-fixtures/json_not_formatted_5.input b/internal/gomodifytags/test-fixtures/json_not_formatted_5.input
similarity index 100%
rename from test-fixtures/json_not_formatted_5.input
rename to internal/gomodifytags/test-fixtures/json_not_formatted_5.input
diff --git a/test-fixtures/json_not_formatted_6.golden b/internal/gomodifytags/test-fixtures/json_not_formatted_6.golden
similarity index 100%
rename from test-fixtures/json_not_formatted_6.golden
rename to internal/gomodifytags/test-fixtures/json_not_formatted_6.golden
diff --git a/test-fixtures/json_not_formatted_6.input b/internal/gomodifytags/test-fixtures/json_not_formatted_6.input
similarity index 100%
rename from test-fixtures/json_not_formatted_6.input
rename to internal/gomodifytags/test-fixtures/json_not_formatted_6.input
diff --git a/test-fixtures/json_single.golden b/internal/gomodifytags/test-fixtures/json_single.golden
similarity index 100%
rename from test-fixtures/json_single.golden
rename to internal/gomodifytags/test-fixtures/json_single.golden
diff --git a/test-fixtures/json_single.input b/internal/gomodifytags/test-fixtures/json_single.input
similarity index 100%
rename from test-fixtures/json_single.input
rename to internal/gomodifytags/test-fixtures/json_single.input
diff --git a/test-fixtures/line_add.golden b/internal/gomodifytags/test-fixtures/line_add.golden
similarity index 100%
rename from test-fixtures/line_add.golden
rename to internal/gomodifytags/test-fixtures/line_add.golden
diff --git a/test-fixtures/line_add.input b/internal/gomodifytags/test-fixtures/line_add.input
similarity index 100%
rename from test-fixtures/line_add.input
rename to internal/gomodifytags/test-fixtures/line_add.input
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similarity index 100%
rename from test-fixtures/line_add_comment.golden
rename to internal/gomodifytags/test-fixtures/line_add_comment.golden
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similarity index 100%
rename from test-fixtures/line_add_comment.input
rename to internal/gomodifytags/test-fixtures/line_add_comment.input
diff --git a/test-fixtures/line_add_intersect_partial.golden b/internal/gomodifytags/test-fixtures/line_add_intersect_partial.golden
similarity index 100%
rename from test-fixtures/line_add_intersect_partial.golden
rename to internal/gomodifytags/test-fixtures/line_add_intersect_partial.golden
diff --git a/test-fixtures/line_add_intersect_partial.input b/internal/gomodifytags/test-fixtures/line_add_intersect_partial.input
similarity index 100%
rename from test-fixtures/line_add_intersect_partial.input
rename to internal/gomodifytags/test-fixtures/line_add_intersect_partial.input
diff --git a/test-fixtures/line_add_multiple_option.golden b/internal/gomodifytags/test-fixtures/line_add_multiple_option.golden
similarity index 100%
rename from test-fixtures/line_add_multiple_option.golden
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similarity index 100%
rename from test-fixtures/line_add_multiple_option.input
rename to internal/gomodifytags/test-fixtures/line_add_multiple_option.input
diff --git a/test-fixtures/line_add_no_override.golden b/internal/gomodifytags/test-fixtures/line_add_no_override.golden
similarity index 100%
rename from test-fixtures/line_add_no_override.golden
rename to internal/gomodifytags/test-fixtures/line_add_no_override.golden
diff --git a/test-fixtures/line_add_no_override.input b/internal/gomodifytags/test-fixtures/line_add_no_override.input
similarity index 100%
rename from test-fixtures/line_add_no_override.input
rename to internal/gomodifytags/test-fixtures/line_add_no_override.input
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similarity index 100%
rename from test-fixtures/line_add_option.golden
rename to internal/gomodifytags/test-fixtures/line_add_option.golden
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similarity index 100%
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rename to internal/gomodifytags/test-fixtures/line_add_option.input
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similarity index 100%
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similarity index 100%
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similarity index 100%
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similarity index 100%
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similarity index 100%
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similarity index 100%
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similarity index 100%
rename from test-fixtures/line_add_override_mixed_column_and_equal.golden
rename to internal/gomodifytags/test-fixtures/line_add_override_mixed_column_and_equal.golden
diff --git a/test-fixtures/line_add_override_mixed_column_and_equal.input b/internal/gomodifytags/test-fixtures/line_add_override_mixed_column_and_equal.input
similarity index 100%
rename from test-fixtures/line_add_override_mixed_column_and_equal.input
rename to internal/gomodifytags/test-fixtures/line_add_override_mixed_column_and_equal.input
diff --git a/test-fixtures/line_add_override_multi_column.golden b/internal/gomodifytags/test-fixtures/line_add_override_multi_column.golden
similarity index 100%
rename from test-fixtures/line_add_override_multi_column.golden
rename to internal/gomodifytags/test-fixtures/line_add_override_multi_column.golden
diff --git a/test-fixtures/line_add_override_multi_column.input b/internal/gomodifytags/test-fixtures/line_add_override_multi_column.input
similarity index 100%
rename from test-fixtures/line_add_override_multi_column.input
rename to internal/gomodifytags/test-fixtures/line_add_override_multi_column.input
diff --git a/test-fixtures/line_add_override_multi_equal.golden b/internal/gomodifytags/test-fixtures/line_add_override_multi_equal.golden
similarity index 100%
rename from test-fixtures/line_add_override_multi_equal.golden
rename to internal/gomodifytags/test-fixtures/line_add_override_multi_equal.golden
diff --git a/test-fixtures/line_add_override_multi_equal.input b/internal/gomodifytags/test-fixtures/line_add_override_multi_equal.input
similarity index 100%
rename from test-fixtures/line_add_override_multi_equal.input
rename to internal/gomodifytags/test-fixtures/line_add_override_multi_equal.input
diff --git a/test-fixtures/line_camelcase_add.golden b/internal/gomodifytags/test-fixtures/line_camelcase_add.golden
similarity index 100%
rename from test-fixtures/line_camelcase_add.golden
rename to internal/gomodifytags/test-fixtures/line_camelcase_add.golden
diff --git a/test-fixtures/line_camelcase_add.input b/internal/gomodifytags/test-fixtures/line_camelcase_add.input
similarity index 100%
rename from test-fixtures/line_camelcase_add.input
rename to internal/gomodifytags/test-fixtures/line_camelcase_add.input
diff --git a/test-fixtures/line_camelcase_add_embedded.golden b/internal/gomodifytags/test-fixtures/line_camelcase_add_embedded.golden
similarity index 100%
rename from test-fixtures/line_camelcase_add_embedded.golden
rename to internal/gomodifytags/test-fixtures/line_camelcase_add_embedded.golden
diff --git a/test-fixtures/line_camelcase_add_embedded.input b/internal/gomodifytags/test-fixtures/line_camelcase_add_embedded.input
similarity index 100%
rename from test-fixtures/line_camelcase_add_embedded.input
rename to internal/gomodifytags/test-fixtures/line_camelcase_add_embedded.input
diff --git a/test-fixtures/line_directive_unix.golden b/internal/gomodifytags/test-fixtures/line_directive_unix.golden
similarity index 100%
rename from test-fixtures/line_directive_unix.golden
rename to internal/gomodifytags/test-fixtures/line_directive_unix.golden
diff --git a/test-fixtures/line_directive_unix.input b/internal/gomodifytags/test-fixtures/line_directive_unix.input
similarity index 100%
rename from test-fixtures/line_directive_unix.input
rename to internal/gomodifytags/test-fixtures/line_directive_unix.input
diff --git a/test-fixtures/line_directive_windows.golden b/internal/gomodifytags/test-fixtures/line_directive_windows.golden
similarity index 100%
rename from test-fixtures/line_directive_windows.golden
rename to internal/gomodifytags/test-fixtures/line_directive_windows.golden
diff --git a/test-fixtures/line_directive_windows.input b/internal/gomodifytags/test-fixtures/line_directive_windows.input
similarity index 100%
rename from test-fixtures/line_directive_windows.input
rename to internal/gomodifytags/test-fixtures/line_directive_windows.input
diff --git a/test-fixtures/line_lispcase_add.golden b/internal/gomodifytags/test-fixtures/line_lispcase_add.golden
similarity index 100%
rename from test-fixtures/line_lispcase_add.golden
rename to internal/gomodifytags/test-fixtures/line_lispcase_add.golden
diff --git a/test-fixtures/line_lispcase_add.input b/internal/gomodifytags/test-fixtures/line_lispcase_add.input
similarity index 100%
rename from test-fixtures/line_lispcase_add.input
rename to internal/gomodifytags/test-fixtures/line_lispcase_add.input
diff --git a/test-fixtures/line_multiple_add.golden b/internal/gomodifytags/test-fixtures/line_multiple_add.golden
similarity index 100%
rename from test-fixtures/line_multiple_add.golden
rename to internal/gomodifytags/test-fixtures/line_multiple_add.golden
diff --git a/test-fixtures/line_multiple_add.input b/internal/gomodifytags/test-fixtures/line_multiple_add.input
similarity index 100%
rename from test-fixtures/line_multiple_add.input
rename to internal/gomodifytags/test-fixtures/line_multiple_add.input
diff --git a/test-fixtures/line_pascalcase_add.golden b/internal/gomodifytags/test-fixtures/line_pascalcase_add.golden
similarity index 100%
rename from test-fixtures/line_pascalcase_add.golden
rename to internal/gomodifytags/test-fixtures/line_pascalcase_add.golden
diff --git a/test-fixtures/line_pascalcase_add.input b/internal/gomodifytags/test-fixtures/line_pascalcase_add.input
similarity index 100%
rename from test-fixtures/line_pascalcase_add.input
rename to internal/gomodifytags/test-fixtures/line_pascalcase_add.input
diff --git a/test-fixtures/line_pascalcase_add_embedded.golden b/internal/gomodifytags/test-fixtures/line_pascalcase_add_embedded.golden
similarity index 100%
rename from test-fixtures/line_pascalcase_add_embedded.golden
rename to internal/gomodifytags/test-fixtures/line_pascalcase_add_embedded.golden
diff --git a/test-fixtures/line_pascalcase_add_embedded.input b/internal/gomodifytags/test-fixtures/line_pascalcase_add_embedded.input
similarity index 100%
rename from test-fixtures/line_pascalcase_add_embedded.input
rename to internal/gomodifytags/test-fixtures/line_pascalcase_add_embedded.input
diff --git a/test-fixtures/line_remove.golden b/internal/gomodifytags/test-fixtures/line_remove.golden
similarity index 100%
rename from test-fixtures/line_remove.golden
rename to internal/gomodifytags/test-fixtures/line_remove.golden
diff --git a/test-fixtures/line_remove.input b/internal/gomodifytags/test-fixtures/line_remove.input
similarity index 100%
rename from test-fixtures/line_remove.input
rename to internal/gomodifytags/test-fixtures/line_remove.input
diff --git a/test-fixtures/line_remove_option.golden b/internal/gomodifytags/test-fixtures/line_remove_option.golden
similarity index 100%
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rename to internal/gomodifytags/test-fixtures/line_remove_option.golden
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similarity index 100%
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rename to internal/gomodifytags/test-fixtures/line_remove_option.input
diff --git a/test-fixtures/line_remove_option_with_equal.golden b/internal/gomodifytags/test-fixtures/line_remove_option_with_equal.golden
similarity index 100%
rename from test-fixtures/line_remove_option_with_equal.golden
rename to internal/gomodifytags/test-fixtures/line_remove_option_with_equal.golden
diff --git a/test-fixtures/line_remove_option_with_equal.input b/internal/gomodifytags/test-fixtures/line_remove_option_with_equal.input
similarity index 100%
rename from test-fixtures/line_remove_option_with_equal.input
rename to internal/gomodifytags/test-fixtures/line_remove_option_with_equal.input
diff --git a/test-fixtures/line_remove_options.golden b/internal/gomodifytags/test-fixtures/line_remove_options.golden
similarity index 100%
rename from test-fixtures/line_remove_options.golden
rename to internal/gomodifytags/test-fixtures/line_remove_options.golden
diff --git a/test-fixtures/line_remove_options.input b/internal/gomodifytags/test-fixtures/line_remove_options.input
similarity index 100%
rename from test-fixtures/line_remove_options.input
rename to internal/gomodifytags/test-fixtures/line_remove_options.input
diff --git a/test-fixtures/line_titlecase_add.golden b/internal/gomodifytags/test-fixtures/line_titlecase_add.golden
similarity index 100%
rename from test-fixtures/line_titlecase_add.golden
rename to internal/gomodifytags/test-fixtures/line_titlecase_add.golden
diff --git a/test-fixtures/line_titlecase_add.input b/internal/gomodifytags/test-fixtures/line_titlecase_add.input
similarity index 100%
rename from test-fixtures/line_titlecase_add.input
rename to internal/gomodifytags/test-fixtures/line_titlecase_add.input
diff --git a/test-fixtures/line_titlecase_add_embedded.golden b/internal/gomodifytags/test-fixtures/line_titlecase_add_embedded.golden
similarity index 100%
rename from test-fixtures/line_titlecase_add_embedded.golden
rename to internal/gomodifytags/test-fixtures/line_titlecase_add_embedded.golden
diff --git a/test-fixtures/line_titlecase_add_embedded.input b/internal/gomodifytags/test-fixtures/line_titlecase_add_embedded.input
similarity index 100%
rename from test-fixtures/line_titlecase_add_embedded.input
rename to internal/gomodifytags/test-fixtures/line_titlecase_add_embedded.input
diff --git a/test-fixtures/line_value_add.golden b/internal/gomodifytags/test-fixtures/line_value_add.golden
similarity index 100%
rename from test-fixtures/line_value_add.golden
rename to internal/gomodifytags/test-fixtures/line_value_add.golden
diff --git a/test-fixtures/line_value_add.input b/internal/gomodifytags/test-fixtures/line_value_add.input
similarity index 100%
rename from test-fixtures/line_value_add.input
rename to internal/gomodifytags/test-fixtures/line_value_add.input
diff --git a/test-fixtures/not_formatted.golden b/internal/gomodifytags/test-fixtures/not_formatted.golden
similarity index 100%
rename from test-fixtures/not_formatted.golden
rename to internal/gomodifytags/test-fixtures/not_formatted.golden
diff --git a/test-fixtures/not_formatted.input b/internal/gomodifytags/test-fixtures/not_formatted.input
similarity index 100%
rename from test-fixtures/not_formatted.input
rename to internal/gomodifytags/test-fixtures/not_formatted.input
diff --git a/test-fixtures/offset_add.golden b/internal/gomodifytags/test-fixtures/offset_add.golden
similarity index 100%
rename from test-fixtures/offset_add.golden
rename to internal/gomodifytags/test-fixtures/offset_add.golden
diff --git a/test-fixtures/offset_add.input b/internal/gomodifytags/test-fixtures/offset_add.input
similarity index 100%
rename from test-fixtures/offset_add.input
rename to internal/gomodifytags/test-fixtures/offset_add.input
diff --git a/test-fixtures/offset_add_composite.golden b/internal/gomodifytags/test-fixtures/offset_add_composite.golden
similarity index 100%
rename from test-fixtures/offset_add_composite.golden
rename to internal/gomodifytags/test-fixtures/offset_add_composite.golden
diff --git a/test-fixtures/offset_add_composite.input b/internal/gomodifytags/test-fixtures/offset_add_composite.input
similarity index 100%
rename from test-fixtures/offset_add_composite.input
rename to internal/gomodifytags/test-fixtures/offset_add_composite.input
diff --git a/test-fixtures/offset_add_duplicate.golden b/internal/gomodifytags/test-fixtures/offset_add_duplicate.golden
similarity index 100%
rename from test-fixtures/offset_add_duplicate.golden
rename to internal/gomodifytags/test-fixtures/offset_add_duplicate.golden
diff --git a/test-fixtures/offset_add_duplicate.input b/internal/gomodifytags/test-fixtures/offset_add_duplicate.input
similarity index 100%
rename from test-fixtures/offset_add_duplicate.input
rename to internal/gomodifytags/test-fixtures/offset_add_duplicate.input
diff --git a/test-fixtures/offset_add_literal_in.golden b/internal/gomodifytags/test-fixtures/offset_add_literal_in.golden
similarity index 100%
rename from test-fixtures/offset_add_literal_in.golden
rename to internal/gomodifytags/test-fixtures/offset_add_literal_in.golden
diff --git a/test-fixtures/offset_add_literal_in.input b/internal/gomodifytags/test-fixtures/offset_add_literal_in.input
similarity index 100%
rename from test-fixtures/offset_add_literal_in.input
rename to internal/gomodifytags/test-fixtures/offset_add_literal_in.input
diff --git a/test-fixtures/offset_add_literal_out.golden b/internal/gomodifytags/test-fixtures/offset_add_literal_out.golden
similarity index 100%
rename from test-fixtures/offset_add_literal_out.golden
rename to internal/gomodifytags/test-fixtures/offset_add_literal_out.golden
diff --git a/test-fixtures/offset_add_literal_out.input b/internal/gomodifytags/test-fixtures/offset_add_literal_out.input
similarity index 100%
rename from test-fixtures/offset_add_literal_out.input
rename to internal/gomodifytags/test-fixtures/offset_add_literal_out.input
diff --git a/test-fixtures/offset_anonymous_struct.golden b/internal/gomodifytags/test-fixtures/offset_anonymous_struct.golden
similarity index 100%
rename from test-fixtures/offset_anonymous_struct.golden
rename to internal/gomodifytags/test-fixtures/offset_anonymous_struct.golden
diff --git a/test-fixtures/offset_anonymous_struct.input b/internal/gomodifytags/test-fixtures/offset_anonymous_struct.input
similarity index 100%
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rename to internal/gomodifytags/test-fixtures/offset_anonymous_struct.input
diff --git a/test-fixtures/offset_array_struct.golden b/internal/gomodifytags/test-fixtures/offset_array_struct.golden
similarity index 100%
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rename to internal/gomodifytags/test-fixtures/offset_array_struct.golden
diff --git a/test-fixtures/offset_array_struct.input b/internal/gomodifytags/test-fixtures/offset_array_struct.input
similarity index 100%
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rename to internal/gomodifytags/test-fixtures/offset_array_struct.input
diff --git a/test-fixtures/offset_star_struct.golden b/internal/gomodifytags/test-fixtures/offset_star_struct.golden
similarity index 100%
rename from test-fixtures/offset_star_struct.golden
rename to internal/gomodifytags/test-fixtures/offset_star_struct.golden
diff --git a/test-fixtures/offset_star_struct.input b/internal/gomodifytags/test-fixtures/offset_star_struct.input
similarity index 100%
rename from test-fixtures/offset_star_struct.input
rename to internal/gomodifytags/test-fixtures/offset_star_struct.input
diff --git a/test-fixtures/skip_embedded.golden b/internal/gomodifytags/test-fixtures/skip_embedded.golden
similarity index 100%
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rename to internal/gomodifytags/test-fixtures/skip_embedded.golden
diff --git a/test-fixtures/skip_embedded.input b/internal/gomodifytags/test-fixtures/skip_embedded.input
similarity index 100%
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rename to internal/gomodifytags/test-fixtures/skip_embedded.input
diff --git a/test-fixtures/skip_private.golden b/internal/gomodifytags/test-fixtures/skip_private.golden
similarity index 100%
rename from test-fixtures/skip_private.golden
rename to internal/gomodifytags/test-fixtures/skip_private.golden
diff --git a/test-fixtures/skip_private.input b/internal/gomodifytags/test-fixtures/skip_private.input
similarity index 100%
rename from test-fixtures/skip_private.input
rename to internal/gomodifytags/test-fixtures/skip_private.input
diff --git a/test-fixtures/skip_private_multiple_names.golden b/internal/gomodifytags/test-fixtures/skip_private_multiple_names.golden
similarity index 100%
rename from test-fixtures/skip_private_multiple_names.golden
rename to internal/gomodifytags/test-fixtures/skip_private_multiple_names.golden
diff --git a/test-fixtures/skip_private_multiple_names.input b/internal/gomodifytags/test-fixtures/skip_private_multiple_names.input
similarity index 100%
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rename to internal/gomodifytags/test-fixtures/skip_private_multiple_names.input
diff --git a/test-fixtures/struct_add.golden b/internal/gomodifytags/test-fixtures/struct_add.golden
similarity index 100%
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rename to internal/gomodifytags/test-fixtures/struct_add.golden
diff --git a/test-fixtures/struct_add.input b/internal/gomodifytags/test-fixtures/struct_add.input
similarity index 100%
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diff --git a/test-fixtures/struct_add_existing.golden b/internal/gomodifytags/test-fixtures/struct_add_existing.golden
similarity index 100%
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rename to internal/gomodifytags/test-fixtures/struct_add_existing.golden
diff --git a/test-fixtures/struct_add_existing.input b/internal/gomodifytags/test-fixtures/struct_add_existing.input
similarity index 100%
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rename to internal/gomodifytags/test-fixtures/struct_add_existing.input
diff --git a/test-fixtures/struct_clear_options.golden b/internal/gomodifytags/test-fixtures/struct_clear_options.golden
similarity index 100%
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rename to internal/gomodifytags/test-fixtures/struct_clear_options.golden
diff --git a/test-fixtures/struct_clear_options.input b/internal/gomodifytags/test-fixtures/struct_clear_options.input
similarity index 100%
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rename to internal/gomodifytags/test-fixtures/struct_clear_options.input
diff --git a/test-fixtures/struct_clear_tags.golden b/internal/gomodifytags/test-fixtures/struct_clear_tags.golden
similarity index 100%
rename from test-fixtures/struct_clear_tags.golden
rename to internal/gomodifytags/test-fixtures/struct_clear_tags.golden
diff --git a/test-fixtures/struct_clear_tags.input b/internal/gomodifytags/test-fixtures/struct_clear_tags.input
similarity index 100%
rename from test-fixtures/struct_clear_tags.input
rename to internal/gomodifytags/test-fixtures/struct_clear_tags.input
diff --git a/test-fixtures/struct_format.golden b/internal/gomodifytags/test-fixtures/struct_format.golden
similarity index 100%
rename from test-fixtures/struct_format.golden
rename to internal/gomodifytags/test-fixtures/struct_format.golden
diff --git a/test-fixtures/struct_format.input b/internal/gomodifytags/test-fixtures/struct_format.input
similarity index 100%
rename from test-fixtures/struct_format.input
rename to internal/gomodifytags/test-fixtures/struct_format.input
diff --git a/test-fixtures/struct_format_existing.golden b/internal/gomodifytags/test-fixtures/struct_format_existing.golden
similarity index 100%
rename from test-fixtures/struct_format_existing.golden
rename to internal/gomodifytags/test-fixtures/struct_format_existing.golden
diff --git a/test-fixtures/struct_format_existing.input b/internal/gomodifytags/test-fixtures/struct_format_existing.input
similarity index 100%
rename from test-fixtures/struct_format_existing.input
rename to internal/gomodifytags/test-fixtures/struct_format_existing.input
diff --git a/test-fixtures/struct_format_existing_oldstyle.golden b/internal/gomodifytags/test-fixtures/struct_format_existing_oldstyle.golden
similarity index 100%
rename from test-fixtures/struct_format_existing_oldstyle.golden
rename to internal/gomodifytags/test-fixtures/struct_format_existing_oldstyle.golden
diff --git a/test-fixtures/struct_format_existing_oldstyle.input b/internal/gomodifytags/test-fixtures/struct_format_existing_oldstyle.input
similarity index 100%
rename from test-fixtures/struct_format_existing_oldstyle.input
rename to internal/gomodifytags/test-fixtures/struct_format_existing_oldstyle.input
diff --git a/test-fixtures/struct_format_oldstyle.golden b/internal/gomodifytags/test-fixtures/struct_format_oldstyle.golden
similarity index 100%
rename from test-fixtures/struct_format_oldstyle.golden
rename to internal/gomodifytags/test-fixtures/struct_format_oldstyle.golden
diff --git a/test-fixtures/struct_format_oldstyle.input b/internal/gomodifytags/test-fixtures/struct_format_oldstyle.input
similarity index 100%
rename from test-fixtures/struct_format_oldstyle.input
rename to internal/gomodifytags/test-fixtures/struct_format_oldstyle.input
diff --git a/test-fixtures/struct_remove.golden b/internal/gomodifytags/test-fixtures/struct_remove.golden
similarity index 100%
rename from test-fixtures/struct_remove.golden
rename to internal/gomodifytags/test-fixtures/struct_remove.golden
diff --git a/test-fixtures/struct_remove.input b/internal/gomodifytags/test-fixtures/struct_remove.input
similarity index 100%
rename from test-fixtures/struct_remove.input
rename to internal/gomodifytags/test-fixtures/struct_remove.input
diff --git a/main.go b/main.go
index e4efff7..47fea30 100644
--- a/main.go
+++ b/main.go
@@ -1,77 +1,14 @@
 package main
 
 import (
-	"bufio"
-	"bytes"
-	"encoding/json"
-	"errors"
 	"flag"
 	"fmt"
-	"go/ast"
-	"go/format"
-	"go/parser"
-	"go/printer"
-	"go/token"
-	"io"
-	"io/ioutil"
 	"os"
-	"sort"
-	"strconv"
 	"strings"
-	"unicode"
 
-	"github.com/fatih/camelcase"
-	"github.com/fatih/structtag"
-	"golang.org/x/tools/go/buildutil"
+	"github.com/fatih/gomodifytags/internal/gomodifytags"
 )
 
-// structType contains a structType node and it's name. It's a convenient
-// helper type, because *ast.StructType doesn't contain the name of the struct
-type structType struct {
-	name string
-	node *ast.StructType
-}
-
-// output is used usually by editors
-type output struct {
-	Start  int      `json:"start"`
-	End    int      `json:"end"`
-	Lines  []string `json:"lines"`
-	Errors []string `json:"errors,omitempty"`
-}
-
-// config defines how tags should be modified
-type config struct {
-	file     string
-	output   string
-	quiet    bool
-	write    bool
-	modified io.Reader
-
-	offset     int
-	structName string
-	fieldName  string
-	line       string
-	start, end int
-	all        bool
-
-	fset *token.FileSet
-
-	remove        []string
-	removeOptions []string
-
-	add                  []string
-	addOptions           []string
-	override             bool
-	skipUnexportedFields bool
-
-	transform   string
-	sort        bool
-	valueFormat string
-	clear       bool
-	clearOption bool
-}
-
 func main() {
 	if err := realMain(); err != nil {
 		fmt.Fprintln(os.Stderr, err.Error())
@@ -88,40 +25,10 @@ func realMain() error {
 		return err
 	}
 
-	err = cfg.validate()
-	if err != nil {
-		return err
-	}
-
-	node, err := cfg.parse()
-	if err != nil {
-		return err
-	}
-
-	start, end, err := cfg.findSelection(node)
-	if err != nil {
-		return err
-	}
-
-	rewrittenNode, errs := cfg.rewrite(node, start, end)
-	if errs != nil {
-		if _, ok := errs.(*rewriteErrors); !ok {
-			return errs
-		}
-	}
-
-	out, err := cfg.format(rewrittenNode, errs)
-	if err != nil {
-		return err
-	}
-
-	if !cfg.quiet {
-		fmt.Println(out)
-	}
-	return nil
+	return cfg.Run()
 }
 
-func parseConfig(args []string) (*config, error) {
+func parseConfig(args []string) (*gomodifytags.Config, error) {
 	var (
 		// file flags
 		flagFile  = flag.String("file", "", "Filename to be parsed")
@@ -183,740 +90,44 @@ func parseConfig(args []string) (*config, error) {
 		return nil, flag.ErrHelp
 	}
 
-	cfg := &config{
-		file:                 *flagFile,
-		line:                 *flagLine,
-		structName:           *flagStruct,
-		fieldName:            *flagField,
-		offset:               *flagOffset,
-		all:                  *flagAll,
-		output:               *flagOutput,
-		write:                *flagWrite,
-		quiet:                *flagQuiet,
-		clear:                *flagClearTags,
-		clearOption:          *flagClearOptions,
-		transform:            *flagTransform,
-		sort:                 *flagSort,
-		valueFormat:          *flagFormatting,
-		override:             *flagOverride,
-		skipUnexportedFields: *flagSkipUnexportedFields,
+	cfg := &gomodifytags.Config{
+		File:                 *flagFile,
+		Line:                 *flagLine,
+		StructName:           *flagStruct,
+		FieldName:            *flagField,
+		Offset:               *flagOffset,
+		All:                  *flagAll,
+		Output:               *flagOutput,
+		Write:                *flagWrite,
+		Quiet:                *flagQuiet,
+		Clear:                *flagClearTags,
+		ClearOption:          *flagClearOptions,
+		Transform:            *flagTransform,
+		Sort:                 *flagSort,
+		ValueFormat:          *flagFormatting,
+		Override:             *flagOverride,
+		SkipUnexportedFields: *flagSkipUnexportedFields,
 	}
 
 	if *flagModified {
-		cfg.modified = os.Stdin
+		cfg.Modified = os.Stdin
 	}
 
 	if *flagAddTags != "" {
-		cfg.add = strings.Split(*flagAddTags, ",")
+		cfg.Add = strings.Split(*flagAddTags, ",")
 	}
 
 	if *flagAddOptions != "" {
-		cfg.addOptions = strings.Split(*flagAddOptions, ",")
+		cfg.AddOptions = strings.Split(*flagAddOptions, ",")
 	}
 
 	if *flagRemoveTags != "" {
-		cfg.remove = strings.Split(*flagRemoveTags, ",")
+		cfg.Remove = strings.Split(*flagRemoveTags, ",")
 	}
 
 	if *flagRemoveOptions != "" {
-		cfg.removeOptions = strings.Split(*flagRemoveOptions, ",")
+		cfg.RemoveOptions = strings.Split(*flagRemoveOptions, ",")
 	}
 
 	return cfg, nil
-
-}
-
-func (c *config) parse() (ast.Node, error) {
-	c.fset = token.NewFileSet()
-	var contents interface{}
-	if c.modified != nil {
-		archive, err := buildutil.ParseOverlayArchive(c.modified)
-		if err != nil {
-			return nil, fmt.Errorf("failed to parse -modified archive: %v", err)
-		}
-		fc, ok := archive[c.file]
-		if !ok {
-			return nil, fmt.Errorf("couldn't find %s in archive", c.file)
-		}
-		contents = fc
-	}
-
-	return parser.ParseFile(c.fset, c.file, contents, parser.ParseComments)
-}
-
-// findSelection returns the start and end position of the fields that are
-// suspect to change. It depends on the line, struct or offset selection.
-func (c *config) findSelection(node ast.Node) (int, int, error) {
-	if c.line != "" {
-		return c.lineSelection(node)
-	} else if c.offset != 0 {
-		return c.offsetSelection(node)
-	} else if c.structName != "" {
-		return c.structSelection(node)
-	} else if c.all {
-		return c.allSelection(node)
-	} else {
-		return 0, 0, errors.New("-line, -offset, -struct or -all is not passed")
-	}
-}
-
-func (c *config) process(fieldName, tagVal string) (string, error) {
-	var tag string
-	if tagVal != "" {
-		var err error
-		tag, err = strconv.Unquote(tagVal)
-		if err != nil {
-			return "", err
-		}
-	}
-
-	tags, err := structtag.Parse(tag)
-	if err != nil {
-		return "", err
-	}
-
-	tags = c.removeTags(tags)
-	tags, err = c.removeTagOptions(tags)
-	if err != nil {
-		return "", err
-	}
-
-	tags = c.clearTags(tags)
-	tags = c.clearOptions(tags)
-
-	tags, err = c.addTags(fieldName, tags)
-	if err != nil {
-		return "", err
-	}
-
-	tags, err = c.addTagOptions(tags)
-	if err != nil {
-		return "", err
-	}
-
-	if c.sort {
-		sort.Sort(tags)
-	}
-
-	res := tags.String()
-	if res != "" {
-		res = quote(tags.String())
-	}
-
-	return res, nil
-}
-
-func (c *config) removeTags(tags *structtag.Tags) *structtag.Tags {
-	if c.remove == nil || len(c.remove) == 0 {
-		return tags
-	}
-
-	tags.Delete(c.remove...)
-	return tags
-}
-
-func (c *config) clearTags(tags *structtag.Tags) *structtag.Tags {
-	if !c.clear {
-		return tags
-	}
-
-	tags.Delete(tags.Keys()...)
-	return tags
-}
-
-func (c *config) clearOptions(tags *structtag.Tags) *structtag.Tags {
-	if !c.clearOption {
-		return tags
-	}
-
-	for _, t := range tags.Tags() {
-		t.Options = nil
-	}
-
-	return tags
-}
-
-func (c *config) removeTagOptions(tags *structtag.Tags) (*structtag.Tags, error) {
-	if c.removeOptions == nil || len(c.removeOptions) == 0 {
-		return tags, nil
-	}
-
-	for _, val := range c.removeOptions {
-		// syntax key=option
-		splitted := strings.Split(val, "=")
-		if len(splitted) < 2 {
-			return nil, errors.New("wrong syntax to remove an option. i.e key=option")
-		}
-
-		key := splitted[0]
-		option := strings.Join(splitted[1:], "=")
-
-		tags.DeleteOptions(key, option)
-	}
-
-	return tags, nil
-}
-
-func (c *config) addTagOptions(tags *structtag.Tags) (*structtag.Tags, error) {
-	if c.addOptions == nil || len(c.addOptions) == 0 {
-		return tags, nil
-	}
-
-	for _, val := range c.addOptions {
-		// syntax key=option
-		splitted := strings.Split(val, "=")
-		if len(splitted) < 2 {
-			return nil, errors.New("wrong syntax to add an option. i.e key=option")
-		}
-
-		key := splitted[0]
-		option := strings.Join(splitted[1:], "=")
-
-		tags.AddOptions(key, option)
-	}
-
-	return tags, nil
-}
-
-func (c *config) addTags(fieldName string, tags *structtag.Tags) (*structtag.Tags, error) {
-	if c.add == nil || len(c.add) == 0 {
-		return tags, nil
-	}
-
-	splitted := camelcase.Split(fieldName)
-	name := ""
-
-	unknown := false
-	switch c.transform {
-	case "snakecase":
-		var lowerSplitted []string
-		for _, s := range splitted {
-			lowerSplitted = append(lowerSplitted, strings.ToLower(s))
-		}
-
-		name = strings.Join(lowerSplitted, "_")
-	case "lispcase":
-		var lowerSplitted []string
-		for _, s := range splitted {
-			lowerSplitted = append(lowerSplitted, strings.ToLower(s))
-		}
-
-		name = strings.Join(lowerSplitted, "-")
-	case "camelcase":
-		var titled []string
-		for _, s := range splitted {
-			titled = append(titled, strings.Title(s))
-		}
-
-		titled[0] = strings.ToLower(titled[0])
-
-		name = strings.Join(titled, "")
-	case "pascalcase":
-		var titled []string
-		for _, s := range splitted {
-			titled = append(titled, strings.Title(s))
-		}
-
-		name = strings.Join(titled, "")
-	case "titlecase":
-		var titled []string
-		for _, s := range splitted {
-			titled = append(titled, strings.Title(s))
-		}
-
-		name = strings.Join(titled, " ")
-	case "keep":
-		name = fieldName
-	default:
-		unknown = true
-	}
-
-	if c.valueFormat != "" {
-		prevName := name
-		name = strings.ReplaceAll(c.valueFormat, "{field}", name)
-		if name == c.valueFormat {
-			// support old style for backward compatibility
-			name = strings.ReplaceAll(c.valueFormat, "$field", prevName)
-		}
-	}
-
-	for _, key := range c.add {
-		splitted = strings.SplitN(key, ":", 2)
-		if len(splitted) >= 2 {
-			key = splitted[0]
-			name = strings.Join(splitted[1:], "")
-		} else if unknown {
-			// the user didn't pass any value but want to use an unknown
-			// transform. We don't return above in the default as the user
-			// might pass a value
-			return nil, fmt.Errorf("unknown transform option %q", c.transform)
-		}
-
-		tag, err := tags.Get(key)
-		if err != nil {
-			// tag doesn't exist, create a new one
-			tag = &structtag.Tag{
-				Key:  key,
-				Name: name,
-			}
-		} else if c.override {
-			tag.Name = name
-		}
-
-		if err := tags.Set(tag); err != nil {
-			return nil, err
-		}
-	}
-
-	return tags, nil
-}
-
-// collectStructs collects and maps structType nodes to their positions
-func collectStructs(node ast.Node) map[token.Pos]*structType {
-	structs := make(map[token.Pos]*structType, 0)
-
-	collectStructs := func(n ast.Node) bool {
-		var t ast.Expr
-		var structName string
-
-		switch x := n.(type) {
-		case *ast.TypeSpec:
-			if x.Type == nil {
-				return true
-
-			}
-
-			structName = x.Name.Name
-			t = x.Type
-		case *ast.CompositeLit:
-			t = x.Type
-		case *ast.ValueSpec:
-			structName = x.Names[0].Name
-			t = x.Type
-		case *ast.Field:
-			// this case also catches struct fields and the structName
-			// therefore might contain the field name (which is wrong)
-			// because `x.Type` in this case is not a *ast.StructType.
-			//
-			// We're OK with it, because, in our case *ast.Field represents
-			// a parameter declaration, i.e:
-			//
-			//   func test(arg struct {
-			//   	Field int
-			//   }) {
-			//   }
-			//
-			// and hence the struct name will be `arg`.
-			if len(x.Names) != 0 {
-				structName = x.Names[0].Name
-			}
-			t = x.Type
-		}
-
-		// if expression is in form "*T" or "[]T", dereference to check if "T"
-		// contains a struct expression
-		t = deref(t)
-
-		x, ok := t.(*ast.StructType)
-		if !ok {
-			return true
-		}
-
-		structs[x.Pos()] = &structType{
-			name: structName,
-			node: x,
-		}
-		return true
-	}
-
-	ast.Inspect(node, collectStructs)
-	return structs
-}
-
-func (c *config) format(file ast.Node, rwErrs error) (string, error) {
-	switch c.output {
-	case "source":
-		var buf bytes.Buffer
-		err := format.Node(&buf, c.fset, file)
-		if err != nil {
-			return "", err
-		}
-
-		if c.write {
-			err = ioutil.WriteFile(c.file, buf.Bytes(), 0)
-			if err != nil {
-				return "", err
-			}
-		}
-
-		return buf.String(), nil
-	case "json":
-		// NOTE(arslan): print first the whole file and then cut out our
-		// selection. The reason we don't directly print the struct is that the
-		// printer is not capable of printing loosy comments, comments that are
-		// not part of any field inside a struct. Those are part of *ast.File
-		// and only printed inside a struct if we print the whole file. This
-		// approach is the sanest and simplest way to get a struct printed
-		// back. Second, our cursor might intersect two different structs with
-		// other declarations in between them. Printing the file and cutting
-		// the selection is the easier and simpler to do.
-		var buf bytes.Buffer
-
-		// this is the default config from `format.Node()`, but we add
-		// `printer.SourcePos` to get the original source position of the
-		// modified lines
-		cfg := printer.Config{Mode: printer.SourcePos | printer.UseSpaces | printer.TabIndent, Tabwidth: 8}
-		err := cfg.Fprint(&buf, c.fset, file)
-		if err != nil {
-			return "", err
-		}
-
-		lines, err := parseLines(&buf)
-		if err != nil {
-			return "", err
-		}
-
-		// prevent selection to be larger than the actual number of lines
-		if c.start > len(lines) || c.end > len(lines) {
-			return "", errors.New("line selection is invalid")
-		}
-
-		out := &output{
-			Start: c.start,
-			End:   c.end,
-			Lines: lines[c.start-1 : c.end],
-		}
-
-		if rwErrs != nil {
-			if r, ok := rwErrs.(*rewriteErrors); ok {
-				for _, err := range r.errs {
-					out.Errors = append(out.Errors, err.Error())
-				}
-			}
-		}
-
-		o, err := json.MarshalIndent(out, "", "  ")
-		if err != nil {
-			return "", err
-		}
-
-		return string(o), nil
-	default:
-		return "", fmt.Errorf("unknown output mode: %s", c.output)
-	}
-}
-
-func (c *config) lineSelection(file ast.Node) (int, int, error) {
-	var err error
-	splitted := strings.Split(c.line, ",")
-
-	start, err := strconv.Atoi(splitted[0])
-	if err != nil {
-		return 0, 0, err
-	}
-
-	end := start
-	if len(splitted) == 2 {
-		end, err = strconv.Atoi(splitted[1])
-		if err != nil {
-			return 0, 0, err
-		}
-	}
-
-	if start > end {
-		return 0, 0, errors.New("wrong range. start line cannot be larger than end line")
-	}
-
-	return start, end, nil
-}
-
-func (c *config) structSelection(file ast.Node) (int, int, error) {
-	structs := collectStructs(file)
-
-	var encStruct *ast.StructType
-	for _, st := range structs {
-		if st.name == c.structName {
-			encStruct = st.node
-		}
-	}
-
-	if encStruct == nil {
-		return 0, 0, errors.New("struct name does not exist")
-	}
-
-	// if field name has been specified as well, only select the given field
-	if c.fieldName != "" {
-		return c.fieldSelection(encStruct)
-	}
-
-	start := c.fset.Position(encStruct.Pos()).Line
-	end := c.fset.Position(encStruct.End()).Line
-
-	return start, end, nil
-}
-
-func (c *config) fieldSelection(st *ast.StructType) (int, int, error) {
-	var encField *ast.Field
-	for _, f := range st.Fields.List {
-		for _, field := range f.Names {
-			if field.Name == c.fieldName {
-				encField = f
-			}
-		}
-	}
-
-	if encField == nil {
-		return 0, 0, errors.New(fmt.Sprintf("struct %q doesn't have field name %q",
-			c.structName, c.fieldName))
-	}
-
-	start := c.fset.Position(encField.Pos()).Line
-	end := c.fset.Position(encField.End()).Line
-
-	return start, end, nil
-}
-
-func (c *config) offsetSelection(file ast.Node) (int, int, error) {
-	structs := collectStructs(file)
-
-	var encStruct *ast.StructType
-	for _, st := range structs {
-		structBegin := c.fset.Position(st.node.Pos()).Offset
-		structEnd := c.fset.Position(st.node.End()).Offset
-
-		if structBegin <= c.offset && c.offset <= structEnd {
-			encStruct = st.node
-			break
-		}
-	}
-
-	if encStruct == nil {
-		return 0, 0, errors.New("offset is not inside a struct")
-	}
-
-	// offset selects all fields
-	start := c.fset.Position(encStruct.Pos()).Line
-	end := c.fset.Position(encStruct.End()).Line
-
-	return start, end, nil
-}
-
-// allSelection selects all structs inside a file
-func (c *config) allSelection(file ast.Node) (int, int, error) {
-	start := 1
-	end := c.fset.File(file.Pos()).LineCount()
-
-	return start, end, nil
-}
-
-func isPublicName(name string) bool {
-	for _, c := range name {
-		return unicode.IsUpper(c)
-	}
-	return false
-}
-
-// rewrite rewrites the node for structs between the start and end
-// positions
-func (c *config) rewrite(node ast.Node, start, end int) (ast.Node, error) {
-	errs := &rewriteErrors{errs: make([]error, 0)}
-
-	rewriteFunc := func(n ast.Node) bool {
-		x, ok := n.(*ast.StructType)
-		if !ok {
-			return true
-		}
-
-		for _, f := range x.Fields.List {
-			line := c.fset.Position(f.Pos()).Line
-
-			if !(start <= line && line <= end) {
-				continue
-			}
-
-			fieldName := ""
-			if len(f.Names) != 0 {
-				for _, field := range f.Names {
-					if !c.skipUnexportedFields || isPublicName(field.Name) {
-						fieldName = field.Name
-						break
-					}
-				}
-			}
-
-			// anonymous field
-			if f.Names == nil {
-				ident, ok := f.Type.(*ast.Ident)
-				if !ok {
-					continue
-				}
-
-				if !c.skipUnexportedFields {
-					fieldName = ident.Name
-				}
-			}
-
-			// nothing to process, continue with next line
-			if fieldName == "" {
-				continue
-			}
-
-			if f.Tag == nil {
-				f.Tag = &ast.BasicLit{}
-			}
-
-			res, err := c.process(fieldName, f.Tag.Value)
-			if err != nil {
-				errs.Append(fmt.Errorf("%s:%d:%d:%s",
-					c.fset.Position(f.Pos()).Filename,
-					c.fset.Position(f.Pos()).Line,
-					c.fset.Position(f.Pos()).Column,
-					err))
-				continue
-			}
-
-			f.Tag.Value = res
-		}
-
-		return true
-	}
-
-	ast.Inspect(node, rewriteFunc)
-
-	c.start = start
-	c.end = end
-
-	if len(errs.errs) == 0 {
-		return node, nil
-	}
-
-	return node, errs
-}
-
-// validate validates whether the config is valid or not
-func (c *config) validate() error {
-	if c.file == "" {
-		return errors.New("no file is passed")
-	}
-
-	if c.line == "" && c.offset == 0 && c.structName == "" && !c.all {
-		return errors.New("-line, -offset, -struct or -all is not passed")
-	}
-
-	if c.line != "" && c.offset != 0 ||
-		c.line != "" && c.structName != "" ||
-		c.offset != 0 && c.structName != "" {
-		return errors.New("-line, -offset or -struct cannot be used together. pick one")
-	}
-
-	if (c.add == nil || len(c.add) == 0) &&
-		(c.addOptions == nil || len(c.addOptions) == 0) &&
-		!c.clear &&
-		!c.clearOption &&
-		(c.removeOptions == nil || len(c.removeOptions) == 0) &&
-		(c.remove == nil || len(c.remove) == 0) {
-		return errors.New("one of " +
-			"[-add-tags, -add-options, -remove-tags, -remove-options, -clear-tags, -clear-options]" +
-			" should be defined")
-	}
-
-	if c.fieldName != "" && c.structName == "" {
-		return errors.New("-field is requiring -struct")
-	}
-
-	return nil
-}
-
-func quote(tag string) string {
-	return "`" + tag + "`"
-}
-
-type rewriteErrors struct {
-	errs []error
-}
-
-func (r *rewriteErrors) Error() string {
-	var buf bytes.Buffer
-	for _, e := range r.errs {
-		buf.WriteString(fmt.Sprintf("%s\n", e.Error()))
-	}
-	return buf.String()
-}
-
-func (r *rewriteErrors) Append(err error) {
-	if err == nil {
-		return
-	}
-
-	r.errs = append(r.errs, err)
-}
-
-// parseLines parses the given buffer and returns a slice of lines
-func parseLines(buf io.Reader) ([]string, error) {
-	var lines []string
-	scanner := bufio.NewScanner(buf)
-	for scanner.Scan() {
-		txt := scanner.Text()
-
-		// check for any line directive and store it for next iteration to
-		// re-construct the original file. If it's not a line directive,
-		// continue consturcting the original file
-		if !strings.HasPrefix(txt, "//line") {
-			lines = append(lines, txt)
-			continue
-		}
-
-		lineNr, err := split(txt)
-		if err != nil {
-			return nil, err
-		}
-
-		for i := len(lines); i < lineNr-1; i++ {
-			lines = append(lines, "")
-		}
-
-		lines = lines[:lineNr-1]
-	}
-
-	if err := scanner.Err(); err != nil {
-		return nil, fmt.Errorf("invalid scanner inputl: %s", err)
-	}
-
-	return lines, nil
-}
-
-// split splits the given line directive and returns the line number
-// see https://golang.org/cmd/compile/#hdr-Compiler_Directives for more
-// information
-// NOTE(arslan): this only splits the line directive that the go.Parser
-// outputs. If the go parser changes the format of the line directive, make
-// sure to fix it in the below function
-func split(line string) (int, error) {
-	for i := len(line) - 1; i >= 0; i-- {
-		if line[i] != ':' {
-			continue
-		}
-
-		nr, err := strconv.Atoi(line[i+1:])
-		if err != nil {
-			return 0, err
-		}
-
-		return nr, nil
-	}
-
-	return 0, fmt.Errorf("couldn't parse line: '%s'", line)
-}
-
-// deref takes an expression, and removes all its leading "*" and "[]"
-// operator. Uuse case : if found expression is a "*t" or "[]t", we need to
-// check if "t" contains a struct expression.
-func deref(x ast.Expr) ast.Expr {
-	switch t := x.(type) {
-	case *ast.StarExpr:
-		return deref(t.X)
-	case *ast.ArrayType:
-		return deref(t.Elt)
-	}
-	return x
 }
diff --git a/main_test.go b/main_test.go
index 1facda4..b9f9205 100644
--- a/main_test.go
+++ b/main_test.go
@@ -1,935 +1,13 @@
 package main
 
 import (
-	"bytes"
-	"errors"
 	"flag"
-	"fmt"
 	"io/ioutil"
-	"os"
-	"path/filepath"
-	"reflect"
-	"strings"
 	"testing"
 )
 
-var update = flag.Bool("update", false, "update golden (.out) files")
-
-// This is the directory where our test fixtures are.
-const fixtureDir = "./test-fixtures"
-
-func TestRewrite(t *testing.T) {
-	test := []struct {
-		cfg  *config
-		file string
-	}{
-		{
-			file: "struct_add",
-			cfg: &config{
-				add:        []string{"json"},
-				output:     "source",
-				structName: "foo",
-				transform:  "snakecase",
-			},
-		},
-		{
-			file: "struct_add_existing",
-			cfg: &config{
-				add:        []string{"json"},
-				output:     "source",
-				structName: "foo",
-				transform:  "snakecase",
-			},
-		},
-		{
-			file: "struct_format",
-			cfg: &config{
-				add:         []string{"gaum"},
-				output:      "source",
-				structName:  "foo",
-				transform:   "snakecase",
-				valueFormat: "field_name={field}",
-			},
-		},
-		{
-			file: "struct_format_existing",
-			cfg: &config{
-				add:         []string{"gaum"},
-				output:      "source",
-				structName:  "foo",
-				transform:   "snakecase",
-				valueFormat: "field_name={field}",
-			},
-		},
-		{
-			file: "struct_format_oldstyle",
-			cfg: &config{
-				add:         []string{"gaum"},
-				output:      "source",
-				structName:  "foo",
-				transform:   "snakecase",
-				valueFormat: "field_name=$field",
-			},
-		},
-		{
-			file: "struct_format_existing_oldstyle",
-			cfg: &config{
-				add:         []string{"gaum"},
-				output:      "source",
-				structName:  "foo",
-				transform:   "snakecase",
-				valueFormat: "field_name=$field",
-			},
-		},
-		{
-			file: "struct_remove",
-			cfg: &config{
-				remove:     []string{"json"},
-				output:     "source",
-				structName: "foo",
-			},
-		},
-		{
-			file: "struct_clear_tags",
-			cfg: &config{
-				clear:      true,
-				output:     "source",
-				structName: "foo",
-			},
-		},
-		{
-			file: "struct_clear_options",
-			cfg: &config{
-				clearOption: true,
-				output:      "source",
-				structName:  "foo",
-			},
-		},
-		{
-			file: "line_add",
-			cfg: &config{
-				add:       []string{"json"},
-				output:    "source",
-				line:      "4",
-				transform: "snakecase",
-			},
-		},
-		{
-			file: "line_add_override",
-			cfg: &config{
-				add:       []string{"json"},
-				output:    "source",
-				line:      "4,5",
-				transform: "snakecase",
-				override:  true,
-			},
-		},
-		{
-			file: "line_add_override_column",
-			cfg: &config{
-				add:       []string{"json:MyBar:bar"},
-				output:    "source",
-				line:      "4,4",
-				transform: "snakecase",
-				override:  true,
-			},
-		},
-		{
-			file: "line_add_override_mixed_column_and_equal",
-			cfg: &config{
-				add:       []string{"json:MyBar:bar:foo=qux"},
-				output:    "source",
-				line:      "4,4",
-				transform: "snakecase",
-				override:  true,
-			},
-		},
-		{
-			file: "line_add_override_multi_equal",
-			cfg: &config{
-				add:       []string{"json:MyBar=bar=foo"},
-				output:    "source",
-				line:      "4,4",
-				transform: "snakecase",
-				override:  true,
-			},
-		},
-		{
-			file: "line_add_override_multi_column",
-			cfg: &config{
-				add:       []string{"json:MyBar:bar:foo"},
-				output:    "source",
-				line:      "4,4",
-				transform: "snakecase",
-				override:  true,
-			},
-		},
-		{
-			file: "line_add_no_override",
-			cfg: &config{
-				add:       []string{"json"},
-				output:    "source",
-				line:      "4,5",
-				transform: "snakecase",
-			},
-		},
-		{
-			file: "line_add_outside",
-			cfg: &config{
-				add:       []string{"json"},
-				output:    "source",
-				line:      "2,8",
-				transform: "snakecase",
-			},
-		},
-		{
-			file: "line_add_outside_partial_start",
-			cfg: &config{
-				add:       []string{"json"},
-				output:    "source",
-				line:      "2,5",
-				transform: "snakecase",
-			},
-		},
-		{
-			file: "line_add_outside_partial_end",
-			cfg: &config{
-				add:       []string{"json"},
-				output:    "source",
-				line:      "5,8",
-				transform: "snakecase",
-			},
-		},
-		{
-			file: "line_add_intersect_partial",
-			cfg: &config{
-				add:       []string{"json"},
-				output:    "source",
-				line:      "5,11",
-				transform: "snakecase",
-			},
-		},
-		{
-			file: "line_add_comment",
-			cfg: &config{
-				add:       []string{"json"},
-				output:    "source",
-				line:      "6,7",
-				transform: "snakecase",
-			},
-		},
-		{
-			file: "line_add_option",
-			cfg: &config{
-				addOptions: []string{"json=omitempty"},
-				output:     "source",
-				line:       "4,7",
-			},
-		},
-		{
-			file: "line_add_option_existing",
-			cfg: &config{
-				addOptions: []string{"json=omitempty"},
-				output:     "source",
-				line:       "6,8",
-			},
-		},
-		{
-			file: "line_add_multiple_option",
-			cfg: &config{
-				addOptions: []string{"json=omitempty", "hcl=squash"},
-				add:        []string{"hcl"},
-				output:     "source",
-				line:       "4,7",
-				transform:  "snakecase",
-			},
-		},
-		{
-			file: "line_add_option_with_equal",
-			cfg: &config{
-				addOptions: []string{"validate=max=32"},
-				add:        []string{"validate"},
-				output:     "source",
-				line:       "4,7",
-				transform:  "snakecase",
-			},
-		},
-		{
-			file: "line_remove",
-			cfg: &config{
-				remove: []string{"json"},
-				output: "source",
-				line:   "5,7",
-			},
-		},
-		{
-			file: "line_remove_option",
-			cfg: &config{
-				removeOptions: []string{"hcl=squash"},
-				output:        "source",
-				line:          "4,8",
-			},
-		},
-		{
-			file: "line_remove_options",
-			cfg: &config{
-				removeOptions: []string{"json=omitempty", "hcl=omitnested"},
-				output:        "source",
-				line:          "4,7",
-			},
-		},
-		{
-			file: "line_remove_option_with_equal",
-			cfg: &config{
-				removeOptions: []string{"validate=max=32"},
-				output:        "source",
-				line:          "4,7",
-			},
-		},
-		{
-			file: "line_multiple_add",
-			cfg: &config{
-				add:       []string{"json"},
-				output:    "source",
-				line:      "5,6",
-				transform: "camelcase",
-			},
-		},
-		{
-			file: "line_lispcase_add",
-			cfg: &config{
-				add:       []string{"json"},
-				output:    "source",
-				line:      "4,6",
-				transform: "lispcase",
-			},
-		},
-		{
-			file: "line_camelcase_add",
-			cfg: &config{
-				add:       []string{"json"},
-				output:    "source",
-				line:      "4,5",
-				transform: "camelcase",
-			},
-		},
-		{
-			file: "line_camelcase_add_embedded",
-			cfg: &config{
-				add:       []string{"json"},
-				output:    "source",
-				line:      "4,6",
-				transform: "camelcase",
-			},
-		},
-		{
-			file: "line_value_add",
-			cfg: &config{
-				add:    []string{"json:foo"},
-				output: "source",
-				line:   "4,6",
-			},
-		},
-		{
-			file: "offset_add",
-			cfg: &config{
-				add:       []string{"json"},
-				output:    "source",
-				offset:    32,
-				transform: "snakecase",
-			},
-		},
-		{
-			file: "offset_add_composite",
-			cfg: &config{
-				add:       []string{"json"},
-				output:    "source",
-				offset:    40,
-				transform: "snakecase",
-			},
-		},
-		{
-			file: "offset_add_duplicate",
-			cfg: &config{
-				add:       []string{"json"},
-				output:    "source",
-				offset:    209,
-				transform: "snakecase",
-			},
-		},
-		{
-			file: "offset_add_literal_in",
-			cfg: &config{
-				add:       []string{"json"},
-				output:    "source",
-				offset:    46,
-				transform: "snakecase",
-			},
-		},
-		{
-			file: "offset_add_literal_out",
-			cfg: &config{
-				add:       []string{"json"},
-				output:    "source",
-				offset:    32,
-				transform: "snakecase",
-			},
-		},
-		{
-			file: "errors",
-			cfg: &config{
-				add:       []string{"json"},
-				output:    "source",
-				line:      "4,7",
-				transform: "snakecase",
-			},
-		},
-		{
-			file: "line_pascalcase_add",
-			cfg: &config{
-				add:       []string{"json"},
-				output:    "source",
-				line:      "4,5",
-				transform: "pascalcase",
-			},
-		},
-		{
-			file: "line_pascalcase_add_embedded",
-			cfg: &config{
-				add:       []string{"json"},
-				output:    "source",
-				line:      "4,6",
-				transform: "pascalcase",
-			},
-		},
-		{
-			file: "not_formatted",
-			cfg: &config{
-				add:       []string{"json"},
-				output:    "source",
-				line:      "3,4",
-				transform: "snakecase",
-			},
-		},
-		{
-			file: "skip_private",
-			cfg: &config{
-				add:                  []string{"json"},
-				output:               "source",
-				structName:           "foo",
-				transform:            "snakecase",
-				skipUnexportedFields: true,
-			},
-		},
-		{
-			file: "skip_private_multiple_names",
-			cfg: &config{
-				add:                  []string{"json"},
-				output:               "source",
-				structName:           "foo",
-				transform:            "snakecase",
-				skipUnexportedFields: true,
-			},
-		},
-		{
-			file: "skip_embedded",
-			cfg: &config{
-				add:                  []string{"json"},
-				output:               "source",
-				structName:           "StationCreated",
-				transform:            "snakecase",
-				skipUnexportedFields: true,
-			},
-		},
-		{
-			file: "all_structs",
-			cfg: &config{
-				add:       []string{"json"},
-				output:    "source",
-				all:       true,
-				transform: "snakecase",
-			},
-		},
-		{
-			file: "line_titlecase_add",
-			cfg: &config{
-				add:       []string{"json"},
-				output:    "source",
-				line:      "4,6",
-				transform: "titlecase",
-			},
-		},
-		{
-			file: "line_titlecase_add_embedded",
-			cfg: &config{
-				add:       []string{"json"},
-				output:    "source",
-				line:      "4,6",
-				transform: "titlecase",
-			},
-		},
-		{
-			file: "field_add",
-			cfg: &config{
-				add:        []string{"json"},
-				output:     "source",
-				structName: "foo",
-				fieldName:  "bar",
-				transform:  "snakecase",
-			},
-		},
-		{
-			file: "field_add_same_line",
-			cfg: &config{
-				add:        []string{"json"},
-				output:     "source",
-				structName: "foo",
-				fieldName:  "qux",
-				transform:  "snakecase",
-			},
-		},
-		{
-			file: "field_add_existing",
-			cfg: &config{
-				add:        []string{"json"},
-				output:     "source",
-				structName: "foo",
-				fieldName:  "bar",
-				transform:  "snakecase",
-			},
-		},
-		{
-			file: "field_clear_tags",
-			cfg: &config{
-				clear:      true,
-				output:     "source",
-				structName: "foo",
-				fieldName:  "bar",
-			},
-		},
-		{
-			file: "field_clear_options",
-			cfg: &config{
-				clearOption: true,
-				output:      "source",
-				structName:  "foo",
-				fieldName:   "bar",
-			},
-		},
-		{
-			file: "field_remove",
-			cfg: &config{
-				remove:     []string{"json"},
-				output:     "source",
-				structName: "foo",
-				fieldName:  "bar",
-			},
-		},
-		{
-			file: "offset_anonymous_struct",
-			cfg: &config{
-				add:       []string{"json"},
-				output:    "source",
-				offset:    45,
-				transform: "camelcase",
-			},
-		},
-		{
-			file: "offset_star_struct",
-			cfg: &config{
-				add:       []string{"json"},
-				output:    "source",
-				offset:    35,
-				transform: "camelcase",
-			},
-		},
-		{
-			file: "offset_array_struct",
-			cfg: &config{
-				add:       []string{"json"},
-				output:    "source",
-				offset:    35,
-				transform: "camelcase",
-			},
-		},
-	}
-
-	for _, ts := range test {
-		t.Run(ts.file, func(t *testing.T) {
-			ts.cfg.file = filepath.Join(fixtureDir, fmt.Sprintf("%s.input", ts.file))
-
-			node, err := ts.cfg.parse()
-			if err != nil {
-				t.Fatal(err)
-			}
-
-			start, end, err := ts.cfg.findSelection(node)
-			if err != nil {
-				t.Fatal(err)
-			}
-
-			rewrittenNode, err := ts.cfg.rewrite(node, start, end)
-			if err != nil {
-				if _, ok := err.(*rewriteErrors); !ok {
-					t.Fatal(err)
-				}
-			}
-
-			out, err := ts.cfg.format(rewrittenNode, err)
-			if err != nil {
-				t.Fatal(err)
-			}
-			got := []byte(out)
-
-			// update golden file if necessary
-			golden := filepath.Join(fixtureDir, fmt.Sprintf("%s.golden", ts.file))
-			if *update {
-				err := ioutil.WriteFile(golden, got, 0644)
-				if err != nil {
-					t.Error(err)
-				}
-				return
-			}
-
-			// get golden file
-			want, err := ioutil.ReadFile(golden)
-			if err != nil {
-				t.Fatal(err)
-			}
-
-			var from []byte
-			if ts.cfg.modified != nil {
-				from, err = ioutil.ReadAll(ts.cfg.modified)
-			} else {
-				from, err = ioutil.ReadFile(ts.cfg.file)
-			}
-			if err != nil {
-				t.Fatal(err)
-			}
-
-			// compare
-			if !bytes.Equal(got, want) {
-				t.Errorf("case %s\ngot:\n====\n\n%s\nwant:\n=====\n\n%s\nfrom:\n=====\n\n%s\n",
-					ts.file, got, want, from)
-			}
-		})
-	}
-}
-
-func TestJSON(t *testing.T) {
-	test := []struct {
-		cfg  *config
-		file string
-		err  error
-	}{
-		{
-			file: "json_single",
-			cfg: &config{
-				add:  []string{"json"},
-				line: "5",
-			},
-		},
-		{
-			file: "json_full",
-			cfg: &config{
-				add:  []string{"json"},
-				line: "4,6",
-			},
-		},
-		{
-			file: "json_intersection",
-			cfg: &config{
-				add:  []string{"json"},
-				line: "5,16",
-			},
-		},
-		{
-			// both small & end range larger than file
-			file: "json_single",
-			cfg: &config{
-				add:  []string{"json"},
-				line: "30,32", // invalid selection
-			},
-			err: errors.New("line selection is invalid"),
-		},
-		{
-			// end range larger than file
-			file: "json_single",
-			cfg: &config{
-				add:  []string{"json"},
-				line: "4,50", // invalid selection
-			},
-			err: errors.New("line selection is invalid"),
-		},
-		{
-			file: "json_errors",
-			cfg: &config{
-				add:  []string{"json"},
-				line: "4,7",
-			},
-		},
-		{
-			file: "json_not_formatted",
-			cfg: &config{
-				add:  []string{"json"},
-				line: "3,4",
-			},
-		},
-		{
-			file: "json_not_formatted_2",
-			cfg: &config{
-				add:  []string{"json"},
-				line: "3,3",
-			},
-		},
-		{
-			file: "json_not_formatted_3",
-			cfg: &config{
-				add:    []string{"json"},
-				offset: 23,
-			},
-		},
-		{
-			file: "json_not_formatted_4",
-			cfg: &config{
-				add:    []string{"json"},
-				offset: 51,
-			},
-		},
-		{
-			file: "json_not_formatted_5",
-			cfg: &config{
-				add:    []string{"json"},
-				offset: 29,
-			},
-		},
-		{
-			file: "json_not_formatted_6",
-			cfg: &config{
-				add:  []string{"json"},
-				line: "2,54",
-			},
-		},
-		{
-			file: "json_all_structs",
-			cfg: &config{
-				add: []string{"json"},
-				all: true,
-			},
-		},
-	}
-
-	for _, ts := range test {
-		t.Run(ts.file, func(t *testing.T) {
-			ts.cfg.file = filepath.Join(fixtureDir, fmt.Sprintf("%s.input", ts.file))
-			// these are explicit and shouldn't be changed for this particular
-			// main test
-			ts.cfg.output = "json"
-			ts.cfg.transform = "camelcase"
-
-			node, err := ts.cfg.parse()
-			if err != nil {
-				t.Fatal(err)
-			}
-
-			start, end, err := ts.cfg.findSelection(node)
-			if err != nil {
-				t.Fatal(err)
-			}
-
-			rewrittenNode, err := ts.cfg.rewrite(node, start, end)
-			if err != nil {
-				if _, ok := err.(*rewriteErrors); !ok {
-					t.Fatal(err)
-				}
-			}
-
-			out, err := ts.cfg.format(rewrittenNode, err)
-			if !reflect.DeepEqual(err, ts.err) {
-				t.Logf("want: %v", ts.err)
-				t.Logf("got: %v", err)
-				t.Fatalf("unexpected error")
-			}
-
-			if ts.err != nil {
-				return
-			}
-
-			got := []byte(out)
-
-			// update golden file if necessary
-			golden := filepath.Join(fixtureDir, fmt.Sprintf("%s.golden", ts.file))
-			if *update {
-				err := ioutil.WriteFile(golden, got, 0644)
-				if err != nil {
-					t.Error(err)
-				}
-				return
-			}
-
-			// get golden file
-			want, err := ioutil.ReadFile(golden)
-			if err != nil {
-				t.Fatal(err)
-			}
-
-			from, err := ioutil.ReadFile(ts.cfg.file)
-			if err != nil {
-				t.Fatal(err)
-			}
-
-			// compare
-			if !bytes.Equal(got, want) {
-				t.Errorf("case %s\ngot:\n====\n\n%s\nwant:\n=====\n\n%s\nfrom:\n=====\n\n%s\n",
-					ts.file, got, want, from)
-			}
-		})
-	}
-}
-
-func TestModifiedRewrite(t *testing.T) {
-	cfg := &config{
-		add:        []string{"json"},
-		output:     "source",
-		structName: "foo",
-		transform:  "snakecase",
-		file:       "struct_add_modified",
-		modified: strings.NewReader(`struct_add_modified
-55
-package foo
-
-type foo struct {
-	bar string
-	t   bool
-}
-`),
-	}
-
-	node, err := cfg.parse()
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	start, end, err := cfg.findSelection(node)
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	rewrittenNode, err := cfg.rewrite(node, start, end)
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	got, err := cfg.format(rewrittenNode, err)
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	golden := filepath.Join(fixtureDir, "struct_add.golden")
-	want, err := ioutil.ReadFile(golden)
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	// compare
-	if !bytes.Equal([]byte(got), want) {
-		t.Errorf("got:\n====\n%s\nwant:\n====\n%s\n", got, want)
-	}
-}
-
-func TestModifiedFileMissing(t *testing.T) {
-	cfg := &config{
-		add:        []string{"json"},
-		output:     "source",
-		structName: "foo",
-		transform:  "snakecase",
-		file:       "struct_add_modified",
-		modified: strings.NewReader(`file_that_doesnt_exist
-55
-package foo
-
-type foo struct {
-	bar string
-	t   bool
-}
-`),
-	}
-
-	_, err := cfg.parse()
-	if err == nil {
-		t.Fatal("expected error")
-	}
-}
-
-func TestParseLines(t *testing.T) {
-	var tests = []struct {
-		file string
-	}{
-		{file: "line_directive_unix"},
-		{file: "line_directive_windows"},
-	}
-
-	for _, ts := range tests {
-		ts := ts
-
-		t.Run(ts.file, func(t *testing.T) {
-			filePath := filepath.Join(fixtureDir, fmt.Sprintf("%s.input", ts.file))
-
-			file, err := os.Open(filePath)
-			if err != nil {
-				t.Fatal(err)
-			}
-			defer file.Close()
-
-			out, err := parseLines(file)
-			if err != nil {
-				t.Fatal(err)
-			}
-
-			toBytes := func(lines []string) []byte {
-				var buf bytes.Buffer
-				for _, line := range lines {
-					buf.WriteString(line + "\n")
-				}
-				return buf.Bytes()
-			}
-
-			got := toBytes(out)
-
-			// update golden file if necessary
-			golden := filepath.Join(fixtureDir, fmt.Sprintf("%s.golden", ts.file))
-
-			if *update {
-				err := ioutil.WriteFile(golden, got, 0644)
-				if err != nil {
-					t.Error(err)
-				}
-				return
-			}
-
-			// get golden file
-			want, err := ioutil.ReadFile(golden)
-			if err != nil {
-				t.Fatal(err)
-			}
-
-			from, err := ioutil.ReadFile(filePath)
-			if err != nil {
-				t.Fatal(err)
-			}
-
-			// compare
-			if !bytes.Equal(got, want) {
-				t.Errorf("case %s\ngot:\n====\n\n%s\nwant:\n=====\n\n%s\nfrom:\n=====\n\n%s\n",
-					ts.file, got, want, from)
-			}
-
-		})
-	}
-}
-
 func TestParseConfig(t *testing.T) {
-	// don't output help message during the test
+	// don't Output help message during the test
 	flag.CommandLine.SetOutput(ioutil.Discard)
 
 	// The flag.CommandLine.Parse() call fails if there are flags re-defined