[Findit] Factoring the gitiles (etc) stuff out into its own directory

appengine/findit/common/test/chromium_deps_test.py

 # Copyright 2014 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 base64
 import collections
 
 from testing_utils import testing
 
+from lib.gitiles import git_repository
 from common import chromium_deps
 from common import deps_parser
-from common import git_repository
-from common import repository
 from common import retry_http_client
 from common import http_client_appengine
 from common.dependency import Dependency, DependencyRoll
 
 
-class DummyGitRepository(repository.Repository):
+class DummyGitRepository(object):
+  """A class for mocking GitRepository.
+
+  N.B., in order to use this class for mocking, every module we want to
+  test with a mock GitRepository must not import that class directly.
+  Instead they must import the git_repository module and rely on dynamic
+  dispatch to resolve the GitRepository attribute. Otherwise those
+  modules will hold direct links to the real GitRepository class, and
+  so won't dispatch into this mock class for our unit tests."""
+
   RESPONSES = {}
 
   def __init__(self, *_):
     pass
 
   def GetSource(self, path, revision):
     return self.RESPONSES.get(path, {}).get(revision, None)
 
 
 class ChromiumDEPSTest(testing.AppengineTestCase):
@@ skipping 248 matching lines @@
             'src/',
             'https://chromium.googlesource.com/chromium/src.git', '4', '5'),
     }
     self.assertEqual(chromium_deps.GetDEPSRollsDict('4', '5', 'all'),
                      expected_deps_rolls_dict)
 
   def testIsChromeVersion(self):
     self.assertTrue(chromium_deps.IsChromeVersion('50.0.1234.1'))
     self.assertFalse(chromium_deps.IsChromeVersion('a.b.c.e'))
     self.assertFalse(chromium_deps.IsChromeVersion('502.021.2.0.123'))