Fix comparison on _message_published without data specified (#28)

* Fix comparison on _message_published without data specified

In HedwigPublishMock._message_published(),
    (data is None or msg.data) == data
should be
    (data is None or msg.data == data)

Instead, simplify the comparison by using as the default for data a
dict subclass that compares equal to any dict.

Add a unit test for the plugin that exercises the case of omitting the
optional data argument.

* Replace .format() with f-string

...after noting that the code doesn't use .format() elsewhere and is
targeted only at 3.6+.

hedwig/testing/pytest_plugin.py

@@ -9,22 +9,32 @@
 __all__ = ['mock_hedwig_publish']
 
 
+class AnyDict(dict):
+    """An object equal to any dict."""
+
+    def __eq__(self, other):
+        return isinstance(other, dict)
+
+    def __repr__(self):
+        return f'{type(self).__name__}()'
+
+
 class HedwigPublishMock(mock.MagicMock):
     """
     Custom mock class used by :meth:`hedwig.testing.pytest_plugin.mock_hedwig_publish` to mock the publisher.
     """
 
     def _message_published(self, msg_type, data: Optional[dict], version: Union[str, StrictVersion]) -> bool:
         return any(
-            msg.type == msg_type and (data is None or msg.data) == data and msg.data_schema_version == version
+            msg.type == msg_type and msg.data == data and msg.data_schema_version == version
             for (msg,), _ in self.call_args_list
         )
 
     def _error_message(self) -> str:
         return pprint.pformat([(msg.type, msg.data, msg.data_schema_version) for (msg,), _ in self.call_args_list])
 
     def assert_message_published(
-        self, msg_type, data: Optional[dict] = None, version: Union[str, StrictVersion] = StrictVersion('1.0')
+        self, msg_type, data: Optional[dict] = AnyDict(), version: Union[str, StrictVersion] = StrictVersion('1.0')
     ) -> None:
         """
         Helper function to check if a Hedwig message with given type, data
@@ -36,7 +46,7 @@ def assert_message_published(
         assert self._message_published(msg_type, data, version), self._error_message()
 
     def assert_message_not_published(
-        self, msg_type, data: Optional[dict] = None, version: Union[str, StrictVersion] = StrictVersion('1.0')
+        self, msg_type, data: Optional[dict] = AnyDict(), version: Union[str, StrictVersion] = StrictVersion('1.0')
     ) -> None:
         """
         Helper function to check that a Hedwig message of given type, data

tests/test_pytest_plugin.py

@@ -49,11 +49,16 @@ def test_mock_hedwig_publish_publish_check_same_type(mock_hedwig_publish, messag
         def test_mock_hedwig_publish_published(mock_hedwig_publish, message):
             message.publish()
             mock_hedwig_publish.assert_message_published(message.type, data=message.data, version=message.data_schema_version)
+
+
+        def test_mock_hedwig_publish_published_without_checking_data(mock_hedwig_publish, message):
+            message.publish()
+            mock_hedwig_publish.assert_message_published(message.type, version=message.data_schema_version)
     """
     )
 
     # run all tests with pytest
     result = testdir.runpytest()
 
     # check that all 3 tests passed
-    result.assert_outcomes(passed=4)
+    result.assert_outcomes(passed=5)