Don't discard stderr.

tests/subprocess2_test.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 subprocess2.py."""
 
 import logging
 import optparse
 import os
@@ skipping 308 matching lines @@
 
   def test_redirect_stderr_to_stdout(self):
     def fn(c, e, un, subp):
       # stderr output into stdout but stdout is not piped.
       proc = subp.Popen(
           e + ['--stderr'], stderr=STDOUT, universal_newlines=un)
       res = proc.communicate(), proc.returncode
       self._check_res(res, None, None, 0)
     self._run_test(fn)
 
+  def test_stderr(self):
+    cmd = ['expr', '1', '/', '0']
+    p1 = subprocess.Popen(cmd, stderr=subprocess.PIPE)
+    p2 = subprocess2.Popen(cmd, stderr=subprocess.PIPE)
+    r1 = p1.communicate()
+    r2 = p2.communicate(timeout=100)
+    self.assertEquals(r1, r2)
+
 
 class S2Test(BaseTestCase):
   # Tests that can only run in subprocess2, e.g. new functionalities.
   # In particular, subprocess2.communicate() doesn't exist in subprocess.
   def _run_test(self, function):
     """Runs tests in 6 combinations:
     - LF output with universal_newlines=False
     - CR output with universal_newlines=False
     - CRLF output with universal_newlines=False
     - LF output with universal_newlines=True
@@ skipping 303 matching lines @@
   return options.return_value
 
 
 if __name__ == '__main__':
   logging.basicConfig(level=
       [logging.WARNING, logging.INFO, logging.DEBUG][
         min(2, sys.argv.count('-v'))])
   if len(sys.argv) > 1 and sys.argv[1] == '--child':
     sys.exit(child_main(sys.argv[2:]))
   unittest.main()