Run "git stash" and "git stash apply" before and after a dry test run.

tools/auto_bisect/bisect_perf_regression_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 os
 import re
 import shutil
 import sys
 import unittest
 
@@ skipping 133 matching lines @@
 def _GenericDryRun(options, print_results=False):
   """Performs a dry run of the bisector.
 
   Args:
     options: Dictionary containing the options for the bisect instance.
     print_results: Boolean telling whether to call FormatAndPrintResults.
 
   Returns:
     The results dictionary as returned by the bisect Run method.
   """
+  _AbortIfThereAreUncommittedChanges()
   # Disable rmtree to avoid deleting local trees.
   old_rmtree = shutil.rmtree
+  shutil.rmtree = lambda path, on_error: None
+  # git reset HEAD may be run during the dry run, which removes staged changes.
   try:
-    shutil.rmtree = lambda path, onerror: None
     bisect_instance = _GetBisectPerformanceMetricsInstance(options)
     results = bisect_instance.Run(
         bisect_instance.opts.command, bisect_instance.opts.bad_revision,
         bisect_instance.opts.good_revision, bisect_instance.opts.metric)
 
     if print_results:
       bisect_instance.printer.FormatAndPrintResults(results)
 
     return results
   finally:
     shutil.rmtree = old_rmtree
 
 
+def _AbortIfThereAreUncommittedChanges():
+  """Exits the test prematurely if there are staged changes."""
+  changes = bisect_utils.CheckRunGit(['status', '--short'])
+  if changes.strip():

[prasadv, 2015/01/27 22:32:32]

What does "CheckRunGit" returns when there is no changes? if None then
changes.strip() will fail.

[qyearsley, 2015/01/27 23:49:01]

CheckRunGit returns an empty string when there are no changes, e.g.:
('', 0)

So, this means calling strip() should be unnecessary. Changed it to not call
strip() and added a comment.

+    print 'There are un-committed changes in the current branch.'
+    print 'Aborting the tests to avoid destroying local changes.'
+    sys.exit(1)
+
+
 class BisectPerfRegressionTest(unittest.TestCase):
   """Test case for other functions and classes in bisect-perf-regression.py."""
 
   def setUp(self):
     self.cwd = os.getcwd()
     os.chdir(os.path.abspath(os.path.join(os.path.dirname(__file__),
                                           os.path.pardir, os.path.pardir)))
 
   def tearDown(self):
     os.chdir(self.cwd)
@@ skipping 457 matching lines @@
          ], (None, 0)),
     ]
     self._SetupRunGitMock(try_cmd)
     bisect_perf_regression._BuilderTryjob(
         git_revision, bot_name, bisect_job_name, patch)
 
 
 if __name__ == '__main__':
   unittest.main()