Fix webkit-patch --help.

third_party/WebKit/Tools/Scripts/webkitpy/tool/webkit_patch_unittest.py

 # Copyright 2016 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import unittest
 
 from webkitpy.common.system.outputcapture import OutputCapture
 from webkitpy.tool.webkit_patch import WebKitPatch
 
 
@@ skipping 12 matching lines @@
     def test_split_args_with_no_options(self):
         self.assertEqual(
             WebKitPatch._split_command_name_from_args(['command', 'arg']),
             ('command', ['arg']))
 
     def test_command_by_name(self):
         tool = WebKitPatch('path')
         self.assertEqual(tool.command_by_name('help').name, 'help')
         self.assertIsNone(tool.command_by_name('non-existent'))
 
-    def test_help(self):
+    def test_help_command(self):
         oc = OutputCapture()
         oc.capture_output()
         tool = WebKitPatch('path')
         tool.main(['tool', 'help'])
         out, err, logs = oc.restore_output()
         self.assertTrue(out.startswith('Usage: '))
         self.assertEqual('', err)
         self.assertEqual('', logs)
+
+    def test_help_argument(self):
+        oc = OutputCapture()
+        oc.capture_output()
+        tool = WebKitPatch('path')
+        try:
+            tool.main(['tool', '--help'])
+        except SystemExit:
+            pass  # optparse calls sys.exit after showing help.
+        finally:
+            out, err, logs = oc.restore_output()
+        self.assertTrue(out.startswith('Usage: '))
+        self.assertEqual('', err)
+        self.assertEqual('', logs)