Fix MockFileSystem.walk and add test.

third_party/WebKit/Tools/Scripts/webkitpy/w3c/test_importer_unittest.py

 # Copyright (C) 2013 Adobe Systems Incorporated. All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions
 # are met:
 #
 # 1. Redistributions of source code must retain the above
 #    copyright notice, this list of conditions and the following
 #    disclaimer.
 # 2. Redistributions in binary form must reproduce the above
@@ skipping 36 matching lines @@
 
 class TestImporterTest(unittest.TestCase):
 
     @staticmethod
     def options(**kwargs):
         """Returns a set of option values for TestImporter."""
         options = {
             "overwrite": False,
             "destination": "w3c",
             "ignore_expectations": False,
+            "dry_run": False,

[qyearsley, 2016/06/02 00:07:14]

This change is not related to this particular fix, so it can be taken out of
this CL.

Note: one way to undo changes to a file in a branch is to run: `git checkout
master <filename>`

         }
         options.update(kwargs)
         return optparse.Values(options)
 
     def test_import_dir_with_no_tests(self):
         host = MockHost()
         host.executive = MockExecutive2(exception=ScriptError(
             "abort: no repository found in '/Volumes/Source/src/wk/Tools/Scripts/webkitpy/w3c'"))
         host.filesystem = MockFileSystem(files=FAKE_FILES)
 
         importer = TestImporter(host, FAKE_SOURCE_DIR, FAKE_REPO_DIR, self.options())
 
         oc = OutputCapture()
         oc.capture_output()
         try:
             importer.do_import()
         finally:
             oc.restore_output()
 
     def test_path_too_long_true(self):
         importer = TestImporter(MockHost(), FAKE_SOURCE_DIR, FAKE_REPO_DIR, self.options())
         self.assertTrue(importer.path_too_long(FAKE_REPO_DIR + '/' + ('x' * 150) + '.html'))
 
     def test_path_too_long_false(self):
         importer = TestImporter(MockHost(), FAKE_SOURCE_DIR, FAKE_REPO_DIR, self.options())
         self.assertFalse(importer.path_too_long(FAKE_REPO_DIR + '/x.html'))
 
     # FIXME: Needs more tests.