gh-135056: Add test for http.server cli --header argument

Author: aisipos

Lib/http/server.py

@@ -1008,6 +1008,7 @@ def test(HandlerClass=BaseHTTPRequestHandler,
         except KeyboardInterrupt:
             print("\nKeyboard interrupt received, exiting.")
             sys.exit(0)
+    return server
 
 
 def _main(args=None):
@@ -1081,7 +1082,7 @@ class HTTPSDualStackServer(DualStackServerMixin, ThreadingHTTPSServer):
 
     ServerClass = HTTPSDualStackServer if args.tls_cert else HTTPDualStackServer
 
-    test(
+    return test(
         HandlerClass=SimpleHTTPRequestHandler,
         ServerClass=ServerClass,
         port=args.port,

Lib/test/test_httpservers.py

@@ -1487,6 +1487,34 @@ def test_unknown_flag(self, _):
         self.assertEqual(stdout.getvalue(), '')
         self.assertIn('error', stderr.getvalue())
 
+    def test_response_headers_arg(self):
+        # with mock.patch.object(
+        #     SimpleHTTPRequestHandler, '__init__'
+        # ) as mock_handler, \
+        # mock.patch.object(
+        #     HTTPServer, 'serve_forever'
+        # ) as mock_serve_forever:
+        with mock.patch.object(
+            HTTPServer, 'serve_forever'
+        ) as mock_serve_forever:
+            httpd = server._main(
+                ['-H', 'X-Test1', 'Test1', '-H', 'X-Test2', 'Test2', '8080']
+            )
+            request_handler_class = httpd.RequestHandlerClass
+            with mock.patch.object(
+                    request_handler_class, '__init__'
+            ) as mock_handler_init:
+                mock_handler_init.return_value = None
+                # finish_request instantiates a request handler class,
+                # ensure response_headers are passed to it
+                httpd.finish_request(mock.Mock(), '127.0.0.1')
+                mock_handler_init.assert_called_once_with(
+                    mock.ANY, mock.ANY, mock.ANY, directory=mock.ANY,
+                    response_headers={
+                        'X-Test1': 'Test1', 'X-Test2': 'Test2'
+                    }
+                )
+
 
 class CommandLineRunTimeTestCase(unittest.TestCase):
     served_data = os.urandom(32)