gh-131178: Add tests for ftplib command-line interface (GH-161080)

* gh-131178: Add tests for ftplib command-line interface

Add unit tests in Lib/test/test_ftplib.py covering the ftplib command-line interface: verifying usage message on empty invocation, subprocess invocation, host connection with debuglevel, directory and passive mode commands, file retrieval, and custom netrc file error handling.

(cherry picked from commit c29f95a)

Co-authored-by: Rudransh Shekhar <kanhaiffco2007@gmail.com>
Co-authored-by: Senthil Kumaran <senthil@python.org>

Author: 2 people

Lib/test/test_ftplib.py

@@ -1188,6 +1188,74 @@ def test__all__(self):
         support.check__all__(self, ftplib, not_exported=not_exported)
 
 
+class CommandLineTest(TestCase):
+    """Tests for the ftplib command-line interface."""
+
+    def test_main_no_arguments_prints_usage(self):
+        with mock.patch('sys.argv', ['ftplib']), \
+             support.captured_stdout() as stdout:
+            with self.assertRaises(SystemExit) as cm:
+                ftplib.test()
+            self.assertEqual(cm.exception.code, 0)
+        output = stdout.getvalue()
+        self.assertIn('Usage:', output)
+        self.assertIn('Options:', output)
+        self.assertIn('Commands:', output)
+
+    @requires_subprocess()
+    def test_subprocess_invocation_no_args(self):
+        from test.support.script_helper import assert_python_ok
+        rc, out, err = assert_python_ok('-m', 'ftplib')
+        self.assertEqual(rc, 0)
+        self.assertIn(b'Usage:', out)
+        self.assertIn(b'Options:', out)
+        self.assertIn(b'Commands:', out)
+        self.assertEqual(err, b'')
+
+    @mock.patch('ftplib.FTP')
+    @mock.patch('netrc.netrc', side_effect=OSError)
+    def test_cli_host_and_debugging(self, mock_netrc, mock_ftp_cls):
+        mock_ftp = mock_ftp_cls.return_value
+        with mock.patch('sys.argv', ['ftplib', '-d', '-d', 'example.com']):
+            ftplib.test()
+        mock_ftp_cls.assert_called_once_with('example.com')
+        mock_ftp.set_debuglevel.assert_called_once_with(2)
+        mock_ftp.login.assert_called_once_with('', '', '')
+        mock_ftp.quit.assert_called_once()
+
+    @mock.patch('ftplib.FTP')
+    @mock.patch('netrc.netrc', side_effect=OSError)
+    def test_cli_commands(self, mock_netrc, mock_ftp_cls):
+        mock_ftp = mock_ftp_cls.return_value
+        with mock.patch('sys.argv', ['ftplib', 'example.com', '-l/pub', '-d/incoming', '-p']):
+            ftplib.test()
+        mock_ftp_cls.assert_called_once_with('example.com')
+        mock_ftp.dir.assert_called_once_with('/pub')
+        mock_ftp.sendcmd.assert_called_once_with('CWD /incoming')
+        mock_ftp.set_pasv.assert_called_once()
+        mock_ftp.quit.assert_called_once()
+
+    @mock.patch('ftplib.FTP')
+    @mock.patch('netrc.netrc', side_effect=OSError)
+    def test_cli_retrieve_file(self, mock_netrc, mock_ftp_cls):
+        mock_ftp = mock_ftp_cls.return_value
+        with mock.patch('sys.argv', ['ftplib', 'example.com', 'testfile.txt']):
+            ftplib.test()
+        mock_ftp.retrbinary.assert_called_once()
+        args, kwargs = mock_ftp.retrbinary.call_args
+        self.assertEqual(args[0], 'RETR testfile.txt')
+        mock_ftp.quit.assert_called_once()
+
+    @mock.patch('ftplib.FTP')
+    @mock.patch('netrc.netrc', side_effect=OSError('file not found'))
+    def test_cli_custom_rcfile_error(self, mock_netrc, mock_ftp_cls):
+        with mock.patch('sys.argv', ['ftplib', '-rnonexistent.netrc', 'example.com']), \
+             support.captured_stderr() as stderr:
+            ftplib.test()
+        self.assertIn("Could not open account file -- using anonymous login.",
+                      stderr.getvalue())
+
+
 def setUpModule():
     thread_info = threading_helper.threading_setup()
     unittest.addModuleCleanup(threading_helper.threading_cleanup, *thread_info)