improved coverage

tests/tests_contrib_logging.py

@@ -5,10 +5,11 @@
 import logging
 import logging.handlers
 import sys
+from contextlib import contextmanager
 from io import StringIO
 
 try:
-    from typing import Optional  # pylint: disable=unused-import
+    from typing import Iterator, List, Optional  # pylint: disable=unused-import
 except ImportError:
     pass
 
@@ -29,7 +30,7 @@
 
 
 class CustomTqdm(tqdm):
-    messages = []
+    messages = []  # type: List[str]
 
     @classmethod
     def write(cls, s, **__):  # pylint: disable=arguments-differ
@@ -188,6 +189,21 @@ def test_use_root_logger_by_default_and_write_to_custom_tqdm(self):
             assert CustomTqdm.messages == ['test']
 
 
+@contextmanager
+def add_capturing_logging_handler(
+    logger  # type: logging.Logger
+):
+    # type: (...) -> Iterator[StringIO]
+    try:
+        previous_handlers = logger.handlers
+        out = StringIO()
+        stream_handler = logging.StreamHandler(out)
+        logger.addHandler(stream_handler)
+        yield out
+    finally:
+        logger.handlers = previous_handlers
+
+
 class TestLoggingTqdm:
     @pytest.mark.parametrize(
         "logger_param,expected_logger",
@@ -201,15 +217,21 @@ def test_should_log_tqdm_output(
         logger_param,  # type: Optional[logging.Logger]
         expected_logger  # type: logging.Logger
     ):
-        try:
-            previous_handlers = expected_logger.handlers
-            out = StringIO()
-            stream_handler = logging.StreamHandler(out)
-            expected_logger.addHandler(stream_handler)
+        with add_capturing_logging_handler(expected_logger) as out:
             with logging_tqdm(total=2, logger=logger_param, mininterval=0) as pbar:
                 pbar.update(1)
-        finally:
-            expected_logger.handlers = previous_handlers
-        last_log_line = out.getvalue().splitlines()[-1]
+            last_log_line = out.getvalue().splitlines()[-1]
         assert '50%' in last_log_line
         assert '1/2' in last_log_line
+
+    def test_should_not_output_before_any_progress(self):
+        with add_capturing_logging_handler(DEFAULT_LOGGER) as out:
+            with logging_tqdm(total=2, mininterval=0) as _:
+                pass
+            assert out.getvalue() == ''
+
+    def test_should_not_output_with_none_msg(self):
+        with add_capturing_logging_handler(DEFAULT_LOGGER) as out:
+            with logging_tqdm(total=2, mininterval=0) as pbar:
+                pbar.display()
+            assert out.getvalue() == ''