Actually make use of the may_prompt flag.

tests/presubmit_unittest.py

 #!/usr/bin/python
 # Copyright (c) 2006-2009 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."""
 
 import exceptions
 import random
 import string
@@ skipping 362 matching lines @@
           ).AndReturn(self.presubmit_text)
     self.mox.ReplayAll()
 
     ci = presubmit.gcl.ChangeInfo(name='mychange', issue=0, patchset=0,
                                   description='\n'.join(description_lines),
                                   files=files)
 
     output = StringIO.StringIO()
     input = StringIO.StringIO('n\n')  # say no to the warning
     self.failIf(presubmit.DoPresubmitChecks(ci, False, True, output, input,
-                                            None, False))
+                                            None, True))
     self.assertEqual(output.getvalue().count('??'), 2)
 
     output = StringIO.StringIO()
     input = StringIO.StringIO('y\n')  # say yes to the warning
     self.failUnless(presubmit.DoPresubmitChecks(ci,
                                                 False,
                                                 True,
                                                 output,
                                                 input,
                                                 None,
-                                                False))
+                                                True))
     self.assertEquals(output.getvalue().count('??'), 2)
 
   def testDoPresubmitChecksNoWarningPromptIfErrors(self):
     join = presubmit.os.path.join
     description_lines = ('Hello there',
                          'this is a change',
                          'NOSUCHKEY=http://tracker/123',
                          'REALLYNOSUCHKEY=http://tracker/123')
     files = [
       ['A', join('haspresubmit', 'blat.cc')],
@@ skipping 981 matching lines @@
     test_result.errors = 0
     self.mox.ReplayAll()
 
     results = presubmit_canned_checks.RunPythonUnitTests(
         input_api, presubmit.OutputApi, ['test_module'])
     self.assertEquals(len(results), 0)
 
 
 if __name__ == '__main__':
   unittest.main()