fix test for python 3.7

Author: dantownsend

piccolo/apps/migrations/commands/backwards.py

@@ -43,7 +43,7 @@ async def run(self) -> MigrationResult:
             app_name=self.app_name
         )
         if len(ran_migration_ids) == 0:
-            # Make sure a status of 0 is returned, as we don't want this
+            # Make sure a success is returned, as we don't want this
             # to appear as an error in automated scripts.
             message = "No migrations to reverse!"
             print(message)

tests/apps/migrations/commands/test_forwards_backwards.py

@@ -120,17 +120,10 @@ def test_backwards_unknown_migration(self, print_: MagicMock):
                 )
             )
 
-        self.assertEqual(
-            len(
-                [
-                    i
-                    for i in print_.mock_calls
-                    if i.args[0].startswith(
-                        "Unrecognized migration name - must be one of "
-                    )
-                ]
-            ),
-            1,
+        self.assertTrue(
+            tuple(print_.mock_calls[0])[1][0].startswith(
+                "Unrecognized migration name - must be one of "
+            )
         )
 
     @patch("piccolo.apps.migrations.commands.backwards.print")