Fixing logging threshold issue for execution tests.

It turns out that the root logger needed to have its level set, as the
root logger's level was propagating to the others.  This is now present
in the context manager, and log messages are being captured as expected
in the tests. RE:#651

ui_tests/test_ui_inputs.py

@@ -1620,30 +1620,42 @@ class OpenWorkspaceTest(_QtTest):
 
 
 @contextlib.contextmanager
-def _capture_logging_messages(logger, records):
+def _capture_logging_messages(logger):
     """Capture logging messages and return them as a list.
 
+    This context manager also sets the root logger's level to
+    ``logging.NOTSET`` and restores the former log level on completion of the
+    context being managed.
+
     Args:
         logger (logging.Logger): A logger instance from python's logging system
-            to which log records should be captured.
+            from which log records should be captured.
-        records (list): A list to which log records should be appended.
 
     Returns:
         ``None``."""
+    # The root logger has a default level of WARNING, but for tests we
+    # want to capture everything.
+    root_logger = logging.getLogger()
+    root_logger_prior_level = root_logger.level
+    root_logger.setLevel(logging.NOTSET)
+
     log_queue = queue.Queue()
     log_queue_handler = logging.handlers.QueueHandler(log_queue)
     log_queue_handler.setLevel(logging.NOTSET)  # capture all logging
     logger.addHandler(log_queue_handler)
-    yield
 
-    log_queue_handler.flush()
+    records = []
-    log_records = []
+    try:
+        yield records
+    finally:
+        # No matter what happens, always restore root logger level.
+        root_logger.setLevel(root_logger_prior_level)
+
     try:
         while True:
             records.append(log_queue.get_nowait())
     except queue.Empty:
         logger.removeHandler(log_queue_handler)
-        pass
 
 
 class ExecutionTest(_QtTest):
@@ -1674,16 +1686,17 @@ class ExecutionTest(_QtTest):
         # register the callback with the finished signal.
         executor.finished.connect(callback)
 
-        log_records = []
+        with _capture_logging_messages(execution_logger) as log_records:
-        with _capture_logging_messages(execution_logger, log_records):
             executor.start()
             thread_event.set()
             executor.join()
             if self.qt_app.hasPendingEvents():
                 self.qt_app.processEvents()
+
         callback.assert_called_once()
         target.assert_called_once()
         target.assert_called_with(*args, **kwargs)
+
         self.assertEqual(len(log_records), 0)
 
     def test_executor_exception(self):
@@ -1713,13 +1726,13 @@ class ExecutionTest(_QtTest):
         # register the callback with the finished signal.
         executor.finished.connect(callback)
 
-        log_records = []
+        with _capture_logging_messages(execution_logger) as log_records:
-        with _capture_logging_messages(execution_logger, log_records):
             executor.start()
             thread_event.set()
             executor.join()
             if self.qt_app.hasPendingEvents():
                 self.qt_app.processEvents()
+
         callback.assert_called_once()
         target.assert_called_once()
         target.assert_called_with(*args, **kwargs)
@@ -1729,11 +1742,9 @@ class ExecutionTest(_QtTest):
                          'Some demo exception')
         self.assertTrue(isinstance(executor.traceback, basestring))
 
-        print(log_records)
+        self.assertEqual(len(log_records), 2)
-        self.assertEqual(len(log_records), 1)
         self.assertIn('failed with exception', log_records[0].msg)
-        # There is supposed to be a second logger message here, but I can't
+        self.assertIn('Execution finished', log_records[1].msg)
-        # figure out why it isn't being added to the queue.
 
     def test_default_args(self):
         from natcap.invest.ui.execution import Executor