SAR-55 Fix date format in get_default_formatter

The `datefmt` string was not being set correctly resulting in the
incorrect output:
```
1|2020-01-13 10:42:42,415.415Z|...
```
instead of:
```
1|2020-01-13T10:42:42.415Z|...
```

Tests now ensure that the output from the default configuration
matches the output from the standalone formatters.

ska_logging/configuration.py

@@ -38,6 +38,7 @@ _FORMAT_STR_WITH_TAGS = (
     "%(message)s"
 )
 
+_FORMAT_STR_DATE = "%Y-%m-%dT%H:%M:%S"
 
 _LOGGING_CONFIG = {
     "version": 1,
@@ -46,7 +47,7 @@ _LOGGING_CONFIG = {
         "default": {
             "()": _UTCFormatter,
             "format": _FORMAT_STR_NO_TAGS,
-            "datefmt": "%Y-%m-%dT%H:%M:%S",
+            "datefmt": _FORMAT_STR_DATE,
         }
     },
     "handlers": {
@@ -94,7 +95,7 @@ def configure_logging(level=None, tags_filter=None, overrides=None):
     """
     config = copy.deepcopy(_LOGGING_CONFIG)
     if overrides:
-        config = _override(config, overrides)
+        config = _override(config, copy.deepcopy(overrides))
     if level:
         config["root"]["level"] = level
     if tags_filter:
@@ -128,7 +129,7 @@ def get_default_formatter(tags=False):
         format_str = _FORMAT_STR_WITH_TAGS
     else:
         format_str = _FORMAT_STR_NO_TAGS
-    return _UTCFormatter(fmt=format_str)
+    return _UTCFormatter(fmt=format_str, datefmt=_FORMAT_STR_DATE)
 
 
 def _override(config, overrides):

tests/test_configuration.py

@@ -67,18 +67,15 @@ RECORDER_OVERRIDES = {
 }
 
 
-@pytest.mark.usefixtures("reset_logging")
-class TestConfigureLogging:
-    """Tests for :func:`~ska_logging.configuration.configure_logging`."""
-
 @pytest.fixture
-    def default_logger(self):
+def default_logger():
     """Return user logger instance with default configuration."""
     configure_logging()
     yield logging.getLogger("ska.test.app")
 
+
 @pytest.fixture
-    def recording_logger(self):
+def recording_logger():
     """Return user logger, including a recording handler.
 
     The additional handler has the name "recorder".  It uses the default formatter,
@@ -91,8 +88,9 @@ class TestConfigureLogging:
     configure_logging(overrides=RECORDER_OVERRIDES)
     yield logging.getLogger("ska.logger")
 
+
 @pytest.fixture
-    def recording_tags_logger(self):
+def recording_tags_logger():
     """Return user logger like :func:`recording_logger`, but including tags filter."""
 
     class MyFilter(logging.Filter):
@@ -103,6 +101,11 @@ class TestConfigureLogging:
     configure_logging(tags_filter=MyFilter, overrides=RECORDER_OVERRIDES)
     yield logging.getLogger("ska.logger")
 
+
+@pytest.mark.usefixtures("reset_logging")
+class TestConfigureLogging:
+    """Tests for :func:`~ska_logging.configuration.configure_logging`."""
+
     def test_includes_console_handler(self, default_logger):
         assert get_named_handler(default_logger, "console")
 
@@ -165,23 +168,34 @@ class TestConfigureLogging:
         assert get_named_handler(logger, "test")
 
 
+@pytest.mark.usefixtures("reset_logging")
 class TestGetDefaultFormatter:
     """Tests for :func:`~ska_logging.configuration.get_default_formatter`."""
 
-    def test_default_no_tags(self):
+    def get_recorded_message(self, logger):
+        logger.info("test message")
+        recorder = get_named_handler(logger, "recorder")
+        record = recorder.records[0]
+        message = recorder.logs[0]
+        return record, message
+
+    def test_default_no_tags(self, recording_logger):
         formatter = get_default_formatter()
-        assert isinstance(formatter, ska_logging.configuration._UTCFormatter)
-        assert formatter._fmt == ska_logging.configuration._FORMAT_STR_NO_TAGS
+        record, message = self.get_recorded_message(recording_logger)
+        actual_log_message = formatter.format(record)
+        assert actual_log_message == message
 
-    def test_get_tags_disabled(self):
+    def test_get_tags_disabled(self, recording_logger):
         formatter = get_default_formatter(tags=False)
-        assert isinstance(formatter, ska_logging.configuration._UTCFormatter)
-        assert formatter._fmt == ska_logging.configuration._FORMAT_STR_NO_TAGS
+        record, message = self.get_recorded_message(recording_logger)
+        actual_log_message = formatter.format(record)
+        assert actual_log_message == message
 
-    def test_get_tags_enabled(self):
+    def test_get_tags_enabled(self, recording_tags_logger):
         formatter = get_default_formatter(tags=True)
-        assert isinstance(formatter, ska_logging.configuration._UTCFormatter)
-        assert formatter._fmt == ska_logging.configuration._FORMAT_STR_WITH_TAGS
+        record, message = self.get_recorded_message(recording_tags_logger)
+        actual_log_message = formatter.format(record)
+        assert actual_log_message == message
 
 
 class TestOverride: