add docstrings for every fixture and test methods

also add tests for missing components

tests/ahriman/application/handlers/test_handler_update.py

@@ -8,6 +8,11 @@ from ahriman.core.configuration import Configuration
 
 
 def _default_args(args: argparse.Namespace) -> argparse.Namespace:
+    """
+    default arguments for these test cases
+    :param args: command line arguments fixture
+    :return: generated arguments for these test cases
+    """
     args.package = []
     args.dry_run = False
     args.no_aur = False