Add a comment explaining why async = 1 in the test

test/units/executor/test_task_executor.py

@@ -220,6 +220,10 @@ class TestTaskExecutor(unittest.TestCase):
         mock_task.changed_when = None
         mock_task.failed_when = None
         mock_task.post_validate.return_value = None
+        # mock_task.async cannot be left unset, because on Python 3 MagicMock()
+        # > 0 raises a TypeError   There are two reasons for using the value 1
+        # here: on Python 2 comparing MagicMock() > 0 returns True, and the
+        # other reason is that if I specify 0 here, the test fails. ;)
         mock_task.async = 1
 
         mock_play_context = MagicMock()