Update early check and tests

giticket/giticket.py

@@ -105,8 +105,8 @@ def main(argv=None):
                         default=underscore_split_mode,
                         choices=[underscore_split_mode, regex_match_mode])
     args = parser.parse_args(argv)
-    if not args.conventionalcommits and not args.format:
-        parser.error('You must provide --format if not using --conventionalcommits')
+    if not args.conventionalcommits and not args.format and not args.to_trailer:
+        parser.error('You must provide --format if not using --conventionalcommits and not --to_trailer')
         return 1
     regex = args.regex or r'[A-Z]+-\d+'  # noqa
     format_string = args.format or '{ticket} {commit_msg}' # noqa

tests/test_giticket.py

@@ -288,3 +288,19 @@ def test_main(mock_update_commit_message, mock_argparse):
                                                        True,
                                                        0,
                                                        False)
+
+
+@mock.patch(TESTING_MODULE + '.update_commit_message')
+def test_main_to_trailer_only_is_allowed(mock_update_commit_message):
+    main(['foo.txt', '--to_trailer'])
+    mock_update_commit_message.assert_called_once_with('foo.txt', r'[A-Z]+-\d+',
+                                                       'underscore_split',
+                                                       '{ticket} {commit_msg}',
+                                                       False,
+                                                       0,
+                                                       True)
+
+
+def test_main_errors_without_format_or_conventionalcommits_or_to_trailer():
+    with pytest.raises(SystemExit):
+        main(['foo.txt'])