git cl checkout: implement for Gerrit + add test.

tests/git_cl_test.py

 #!/usr/bin/env python
 # Copyright (c) 2012 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.
 
 """Unit tests for git_cl.py."""
 
 import os
 import StringIO
 import stat
@@ skipping 1133 matching lines @@
          'refs/changes/56/123456/1'],), ''),
       ((['git', 'cherry-pick', 'FETCH_HEAD'],),
         '', subprocess2.CalledProcessError(1, '', '', '', '')),
       ((['DieWithError', 'git cherry-pick FETCH_HEAD" failed.\n'],),
         '', SystemExitMock()),
     ]
     with self.assertRaises(SystemExitMock):
       git_cl.main(['patch',
                    'https://chromium-review.googlesource.com/#/c/123456/1'])
 
+  def _checkout_calls(self):
+    return [
+        ((['git', 'config', '--local', '--get-regexp',
+           'branch\\..*\\.rietveldissue'], ),
+           ('branch.retrying.rietveldissue 1111111111\n'
+            'branch.some-fix.rietveldissue 2222222222\n')),
+        ((['git', 'config', '--local', '--get-regexp',
+           'branch\\..*\\.gerritissue'], ),
+           ('branch.ger-branch.gerritissue 123456\n'
+            'branch.gbranch654.gerritissue 654321\n')),
+    ]
+
+  def test_checkout_gerrit(self):
+    """Tests git cl checkout <issue>."""
+    self.calls = self._checkout_calls()
+    self.calls += [((['git', 'checkout', 'ger-branch'], ), '')]
+    self.assertEqual(0, git_cl.main(['checkout', '123456']))
+
+  def test_checkout_rietveld(self):
+    """Tests git cl checkout <issue>."""
+    self.calls = self._checkout_calls()
+    self.calls += [((['git', 'checkout', 'some-fix'], ), '')]
+    self.assertEqual(0, git_cl.main(['checkout', '2222222222']))
+
+  def test_checkout_not_found(self):
+    """Tests git cl checkout <issue>."""
+    self.calls = self._checkout_calls()
+    self.assertEqual(1, git_cl.main(['checkout', '99999']))
+
 
 if __name__ == '__main__':
   git_cl.logging.basicConfig(
       level=git_cl.logging.DEBUG if '-v' in sys.argv else git_cl.logging.ERROR)
   unittest.main()