Fix a typo that resulted in no tests to be run in depot_tools. :(

PRESUBMIT.py

 # Copyright (c) 2011 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.
 
 """Top-level presubmit script for depot tools.
 
 See http://dev.chromium.org/developers/how-tos/depottools/presubmit-scripts for
 details on the presubmit API built into depot_tools.
 """
 
@@ skipping 24 matching lines @@
       output_api,
       white_list=[r'.*\.py$'],
       black_list=black_list))
 
   # TODO(maruel): Make sure at least one file is modified first.
   # TODO(maruel): If only tests are modified, only run them.
   results.extend(input_api.canned_checks.RunUnitTestsInDirectory(
       input_api,
       output_api,
       'tests',
-      whitelist=[r'.*tests\.py$'],
+      whitelist=[r'.*test\.py$'],
       blacklist=tests_to_black_list))
   return results
 
 
 def RunGitClTests(input_api, output_api):
   """Run all the shells scripts in the directory test.
   """
   if input_api.platform == 'win32':
     # Skip for now as long as the test scripts are bash scripts.
     return []
@@ skipping 51 matching lines @@
 
 
 def CheckChangeOnCommit(input_api, output_api):
   output = []
   output.extend(CommonChecks(input_api, output_api, []))
   output.extend(input_api.canned_checks.CheckDoNotSubmit(
       input_api,
       output_api))
   output.extend(RunGitClTests(input_api, output_api))
   return output