Fix a failure in testDirectoryHandling on posix.

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 os
 import StringIO
 import unittest
 
 # Local imports
 import presubmit_support as presubmit
 import presubmit_canned_checks
 import super_mox
 from super_mox import mox
 
 
@@ skipping 373 matching lines @@
     # Always fail.
     change = presubmit.Change('mychange', '\n'.join(description_lines),
                               self.fake_root_dir, files, 0, 0)
     self.failIf(presubmit.DoPresubmitChecks(change, False, True, output, input,
                                             DEFAULT_SCRIPT, False))
     self.assertEquals(output.getvalue().count('!!'), 1)
 
   def testDirectoryHandling(self):
     files = [
       ['A', 'isdir'],
-      ['A', 'isdir\\blat.cc'],
+      ['A', os.path.join('isdir', 'blat.cc')],
     ]
     isdir = presubmit.os.path.join(self.fake_root_dir, 'isdir')
     blat = presubmit.os.path.join(isdir, 'blat.cc')
     presubmit.os.path.exists(isdir).AndReturn(True)
     presubmit.os.path.isdir(isdir).AndReturn(True)
     presubmit.os.path.exists(blat).AndReturn(True)
     presubmit.os.path.isdir(blat).AndReturn(False)
     self.mox.ReplayAll()
 
     change = presubmit.Change('mychange', 'foo', self.fake_root_dir, files,
@@ skipping 940 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()