add CLI test

Signed-off-by: Florian Brandes <florian.brandes@posteo.de>

smtprd_ng/smtprd.py

@@ -400,11 +400,16 @@ class SMTPServer(Controller):
         return True
 
 
-def main() -> int:
-    """Main routine
+def parse_args(args=None) -> argparse.ArgumentParser.parse_args:
+    """Parse arguments
 
-    Returns:
-        int: exit code
+    Parameters
+    ----------
+    args : List of strings
+
+    Returns
+    -------
+    argparse.ArgumentParser.parse_args : Namespace of arguments
     """
     parser = argparse.ArgumentParser(
         description=__doc__.strip(),
@@ -417,9 +422,21 @@ def main() -> int:
         default="./config.ini",
         help="configuration file",
     )
-    args = parser.parse_args()
-    setlocale(LC_ALL, "C")  # for strftime
+    return parser.parse_args(args)
 
+
+def main(args=None) -> int:
+    """Main routine
+
+    Returns:
+        int: exit code
+    """
+    args = parse_args(args)
+    setlocale(LC_ALL, "C")  # for strftime
+    if len(args.config) == 0:
+        raise OSError("No config file supplied")
+    if not Path(args.config).is_file():
+        raise OSError("Config file not found: " + str(args.config))
     try:
         config: Config = Config.from_ini(args.config)
     except RuntimeError as e: