Add basic test for message reader class

Although this is partially covered by the functional tests of the
CLI [^1], this test adds more coverage by not specifying a limit
of the samples to collect.

[^1]: https://github.com/benthorner/PyPMS/blob/f71628418e4a9d4ab89eea356926b4f158a76e7a/tests/test_cli.py#L32-L45

src/pms/core/reader.py

@@ -203,7 +203,7 @@ def __call__(self, *, raw: Optional[bool] = None):
         for row in self.data:
             time, message = int(row["time"]), bytes.fromhex(row["hex"])
             yield RawData(time, message) if raw else self.sensor.decode(message, time=time)
-            if self.samples:  # pragma: no cover
+            if self.samples:
                 self.samples -= 1
                 if self.samples <= 0:
                     break

tests/core/test_reader.py

@@ -1,6 +1,8 @@
 import pytest
 
 from pms.core import reader
+from pms.core.sensor import Sensor
+from tests.conftest import captured_data
 
 
 class MockReader(reader.Reader):
@@ -162,3 +164,15 @@ def sys_exit(*_args):
             raise Exception("should not get here")
 
     assert "exit" in str(e.value)
+
+
+def test_message_reader():
+    message_reader = reader.MessageReader(
+        path=captured_data,
+        sensor=Sensor["PMS3003"],
+    )
+
+    with message_reader:
+        values = list(message_reader())
+
+    assert len(values) == 10