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

presubmit_canned_checks.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.
 
 """Generic presubmit checks that can be reused by other presubmit checks."""
 
 
 ### Description checks
 
 def CheckChangeHasTestField(input_api, output_api):
@@ skipping 459 matching lines @@
   It's mainly a wrapper for RunUnitTests. USe whitelist and blacklist to filter
   tests accordingly.
   """
   unit_tests = []
   test_path = input_api.os_path.abspath(
       input_api.os_path.join(input_api.PresubmitLocalPath(), directory))
 
   def check(filename, filters):
     return any(True for i in filters if input_api.re.match(i, filename))
 
+  to_run = found = 0
   for filename in input_api.os_listdir(test_path):
+    found += 1
     fullpath = input_api.os_path.join(test_path, filename)
     if not input_api.os_path.isfile(fullpath):
       continue
     if whitelist and not check(filename, whitelist):
       continue
     if blacklist and check(filename, blacklist):
       continue
     unit_tests.append(input_api.os_path.join(directory, filename))
+    to_run += 1
+  input_api.logging.debug('Found %d files, running %d' % (found, to_run))
+  if not to_run:
+    return [
+        output_api.PresubmitPromptWarning(
+          'Out of %d files, found none that matched w=%r, b=%r in directory %s'
+          % (found, whitelist, blacklist, directory))
+    ]
   return RunUnitTests(input_api, output_api, unit_tests)
 
 
 def RunUnitTests(input_api, output_api, unit_tests):
   """Runs all unit tests in a directory.
 
   On Windows, sys.executable is used for unit tests ending with ".py".
   """
   # We don't want to hinder users from uploading incomplete patches.
   if input_api.is_committing:
@@ skipping 443 matching lines @@
     results.extend(input_api.canned_checks.CheckSvnForCommonMimeTypes(
         input_api, output_api))
     snapshot("checking license")
     results.extend(input_api.canned_checks.CheckLicense(
         input_api, output_api, license_header, source_file_filter=sources))
     snapshot("checking was uploaded")
     results.extend(input_api.canned_checks.CheckChangeWasUploaded(
         input_api, output_api))
   snapshot("done")
   return results