Exit with simple_backup()'s return code when run as a script

tests/test_cli.py

@@ -2,6 +2,8 @@
 
 import os
 import pwd
+import subprocess
+import sys
 from collections.abc import Callable
 from pathlib import Path
 from typing import Any
@@ -325,6 +327,20 @@ class TestDetectUser:
         assert sb._detect_user() == USER
 
 
+def test_run_as_script(tmp_path: Path) -> None:
+    """Running the module directly passes simple_backup()'s return code to the shell"""
+
+    repo = Path(sb.__file__).resolve().parents[1]
+    env = {**os.environ, 'PYTHONPATH': str(repo), 'HOME': str(tmp_path)}
+
+    # No config file and no inputs: check_params() returns 1
+    result = subprocess.run([sys.executable, '-m', 'simple_backup.simple_backup', '--no-syslog',
+                             '-c', str(tmp_path / 'missing.conf')], env=env, cwd=tmp_path,
+                            capture_output=True, check=False)
+
+    assert result.returncode == 1
+
+
 class TestTargetUid:
     @pytest.mark.usefixtures('as_user')
     def test_non_root(self) -> None: