Perform Git operations without changing CWD.

unittests/package_test.py

 #!/usr/bin/env python
 # Copyright 2015 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 doctest
 import os
+import subprocess
 import sys
 import unittest
 
 ROOT_DIR = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
 THIRD_PARTY = os.path.join(ROOT_DIR, 'recipe_engine', 'third_party')
 sys.path.insert(0, os.path.join(THIRD_PARTY, 'mock-1.0.1'))
 sys.path.insert(0, THIRD_PARTY)
 sys.path.insert(0, ROOT_DIR)
 
 import mock
 from recipe_engine import package
 
 class MockIOThings(object):
   def setUp(self):
     self.mock_os_patcher = mock.patch('recipe_engine.package.os')
     self.mock_os = self.mock_os_patcher.start()
     self.mock_os.path.join = os.path.join
     self.mock_os.path.dirname = os.path.dirname
     self.mock_os.sep = os.sep
 
+    self.orig_subprocess = subprocess
     self.mock_subprocess_patcher = mock.patch(
         'recipe_engine.package.subprocess')
     self.mock_subprocess = self.mock_subprocess_patcher.start()
+    self.mock_subprocess.PIPE = self.orig_subprocess.PIPE
 
   def tearDown(self):
     self.mock_subprocess_patcher.stop()
     self.mock_os_patcher.stop()
 
 
 class TestGitRepoSpec(MockIOThings, unittest.TestCase):
   REPO_URL = 'https://funny.recipes/repo.git'
   def setUp(self):
     super(TestGitRepoSpec, self).setUp()
@@ skipping 11 matching lines @@
       repo_root='repo/root',
       allow_fetch=False,
     )
 
   def test_checkout_nonexistant_package_dir(self):
     self.mock_os.path.exists.return_value = False
     self.mock_os.path.isdir.return_value = False
 
     self.repo_spec.checkout(self.context)
 
-    self.mock_subprocess.check_call.assert_any_call(
+    self.mock_subprocess.check_output.assert_any_call(
         ['git', 'clone', self.REPO_URL,
-         os.path.join(self.context.package_dir, 'funny_recipes')],
-         cwd=None)
-    self.mock_subprocess.check_call.assert_any_call(
-        ['git', 'reset', '-q', '--hard', 'deadbeef'],
-        cwd='repo/root/recipes/.recipe_deps/funny_recipes')
+         os.path.join(self.context.package_dir, 'funny_recipes')])
+    self.mock_subprocess.check_output.assert_any_call(
+        ['git',
+         '--git-dir', 'repo/root/recipes/.recipe_deps/funny_recipes/.git',
+         'reset', '-q', '--hard', 'deadbeef'])
 
 
 class MockProtoFile(package.ProtoFile):
   def __init__(self, path, text):
     super(MockProtoFile, self).__init__(path)
     self._text = text
 
   @property
   def path(self):
     return self._path
@@ skipping 130 matching lines @@
     self.assertEqual(foo_deps.repo_spec.path, '/path/to/local/foo')
 
 
 def load_tests(_loader, tests, _ignore):
   tests.addTests(doctest.DocTestSuite(package))
   return tests
 
 
 if __name__ == '__main__':
   result = unittest.main()