Add skip_canned option to presubmit_support.

tests/presubmit_unittest.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 presubmit_support.py and presubmit_canned_checks.py."""
 
 # pylint: disable=E1101,E1103
 
 import logging
@@ skipping 141 matching lines @@
   """General presubmit_support.py tests (excluding InputApi and OutputApi)."""
 
   _INHERIT_SETTINGS = 'inherit-review-settings-ok'
 
   def testMembersChanged(self):
     self.mox.ReplayAll()
     members = [
       'AffectedFile', 'Change', 'DoGetTrySlaves', 'DoPresubmitChecks',
       'GetTrySlavesExecuter', 'GitAffectedFile',
       'GitChange', 'InputApi', 'ListRelevantPresubmitFiles', 'Main',
-      'OutputApi', 'ParseFiles', 'PresubmitFailure',
-      'PresubmitExecuter', 'PresubmitOutput', 'ScanSubDirs',
-      'SvnAffectedFile', 'SvnChange', 'cPickle', 'cStringIO',
-      'fix_encoding', 'fnmatch', 'gclient_utils', 'glob', 'inspect', 'json',
-      'load_files',
+      'NonexistantCannedCheckFilter', 'OutputApi', 'ParseFiles',
+      'PresubmitFailure', 'PresubmitExecuter', 'PresubmitOutput', 'ScanSubDirs',
+      'SvnAffectedFile', 'SvnChange', 'cPickle', 'cStringIO', 'contextlib',
+      'canned_check_filter', 'fix_encoding', 'fnmatch', 'gclient_utils', 'glob',
+      'inspect', 'json', 'load_files',
       'logging', 'marshal', 'normpath', 'optparse', 'os', 'owners', 'pickle',
       'presubmit_canned_checks', 'random', 're', 'rietveld', 'scm',
       'subprocess',
       'sys', 'tempfile', 'time', 'traceback', 'types', 'unittest', 'urllib2',
       'warn',
     ]
     # If this test fails, you should add the relevant test.
     self.compareMembers(presubmit, members)
 
+  def testCannedCheckFilter(self):
+    canned = presubmit.presubmit_canned_checks
+    orig = canned.CheckOwners
+    with presubmit.canned_check_filter(['CheckOwners']):
+      self.assertNotEqual(canned.CheckOwners, orig)
+      self.assertEqual(canned.CheckOwners(None, None), [])
+    self.assertEqual(canned.CheckOwners, orig)
+
+  def testCannedCheckFilterFail(self):
+    canned = presubmit.presubmit_canned_checks
+    orig = canned.CheckOwners
+    def failAttempt():
+      with presubmit.canned_check_filter(['CheckOwners', 'Spazfleem']):
+        pass
+    self.assertRaises(presubmit.NonexistantCannedCheckFilter, failAttempt)
+    self.assertEqual(canned.CheckOwners, orig)
+
   def testListRelevantPresubmitFiles(self):
     join = presubmit.os.path.join
     files = [
       'blat.cc',
       join('foo', 'haspresubmit', 'yodle', 'smart.h'),
       join('moo', 'mat', 'gat', 'yo.h'),
       join('foo', 'luck.h'),
     ]
     inherit_path = presubmit.os.path.join(self.fake_root_dir,
                                           self._INHERIT_SETTINGS)
@@ skipping 2318 matching lines @@
         owners_check=False)
     self.assertEqual(1, len(results))
     self.assertEqual(
         'Found line ending with white spaces in:', results[0]._message)
     self.checkstdout('')
 
 
 if __name__ == '__main__':
   import unittest
   unittest.main()