git-squash-branch: handle empty squashes and dirty trees

testing_support/git_test_utils.py

 # Copyright 2013 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 atexit
 import collections
 import copy
 import datetime
 import hashlib
 import os
@@ skipping 331 matching lines @@
           val = commit_data[key]
         else:
           if suffix == 'DATE':
             val = self._date
             self._date += datetime.timedelta(days=1)
           else:
             val = getattr(self, 'DEFAULT_%s' % singleton)
         env['GIT_%s' % singleton] = str(val)
     return env
 
-
   def git(self, *args, **kwargs):
     """Runs a git command specified by |args| in this repo."""
     assert self.repo_path is not None
     try:
       with open(os.devnull, 'wb') as devnull:
         output = subprocess.check_output(
           ('git',) + args, cwd=self.repo_path, stderr=devnull, **kwargs)
       return self.COMMAND_OUTPUT(0, output)
     except subprocess.CalledProcessError as e:
       return self.COMMAND_OUTPUT(e.returncode, e.output)
@@ skipping 135 matching lines @@
     super(GitRepoReadWriteTestBase, self).setUp()
     self.repo = self.r_schema.reify()
 
   def tearDown(self):
     self.repo.nuke()
     super(GitRepoReadWriteTestBase, self).tearDown()
 
   def assertSchema(self, schema_string):
     self.assertEqual(GitRepoSchema(schema_string).simple_graph(),
                      self.repo.to_schema().simple_graph())