Add new test cases and update README

README.md

@@ -57,6 +57,24 @@ Will fail because of method signature mismatch:
         - expected arguments: (req, req)
         - actual arguments: (req, opt=)
 
+Classes may define additional optional or rest arguments.
+
+```ruby
+module Carrier
+  def call(number); end
+
+  def text(number, text); end
+end
+
+class Giffgaff
+  def call(number, *opts); end
+
+  def text(number, text, opt1 = nil, opt2 = nil); end
+end
+```
+
+This will not generate any errors since `Giffgaff` implements the required methods with correct arguments only adding new optional ones.
+
 ### Rails
 
 Mix in `Interfaceable` before any of the application code is loaded. For example, in the initializer. For extra peace of mind, you can noop interface checking in production:

spec/implementation_check_spec.rb

@@ -49,18 +49,9 @@ def foo(aaa, baz = 3, bar:, fuga: 2); end
         }
       }
     )
+  end
 
-    interface = Module.new do
-      def foo(aaa, bbb); end
-    end
-    klass = Class.new do
-      def foo(aaa, baz); end
-    end
-
-    errors = Interfaceable::ImplementationCheck.new(klass).perform([interface])
-
-    expect(errors).to be_empty
-
+  it 'accepts additional optional arguments' do
     interface = Module.new do
       def foo(aaa, bbb); end
     end
@@ -125,15 +116,9 @@ def self.foo(aaa, bar = 1); end
         }
       }
     )
+  end
 
-    klass = Class.new do
-      def self.foo(aaa, bar = 1, *args); end
-    end
-
-    errors = Interfaceable::ImplementationCheck.new(klass).perform([interface])
-
-    expect(errors).to be_empty
-
+  it 'accepts additional *rest argument' do
     interface = Module.new do
       def self.foo(aaa, baz = 3); end
     end
@@ -148,25 +133,9 @@ def self.foo(aaa, bar = 1, *args); end
   end
 
   it 'checks **opts argument' do
-    interface = Module.new do
-      def foo(aaa, baz = 3, *args, foo:); end
-    end
-    klass = Class.new do
-      def foo(aaa, bar = 1, *args, foo:, **opts); end
-    end
-
-    errors = Interfaceable::ImplementationCheck.new(klass).perform([interface])
-
-    # allow the class to have additional rest parameters
-    expect(errors).to be_empty
-
     interface = Module.new do
       def foo(aaa, baz = 3, *args, foo:, **options); end
     end
-
-    errors = Interfaceable::ImplementationCheck.new(klass).perform([interface])
-    expect(errors).to be_empty
-
     klass = Class.new do
       def foo(aaa, bar = 1, *args, foo:); end
     end
@@ -181,5 +150,19 @@ def foo(aaa, bar = 1, *args, foo:); end
       }
     )
   end
+
+  it 'accepts additional **opts argument' do
+    interface = Module.new do
+      def foo(aaa, baz = 3, *args, foo:); end
+    end
+    klass = Class.new do
+      def foo(aaa, bar = 1, *args, foo:, **opts); end
+    end
+
+    errors = Interfaceable::ImplementationCheck.new(klass).perform([interface])
+
+    # allow the class to have additional rest parameters
+    expect(errors).to be_empty
+  end
 end
 # rubocop:enable Metrics/BlockLength