Add subprocess2 unit tests

subprocess2.py

 # coding=utf8
 # 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.
 """Collection of subprocess wrapper functions.
 
 In theory you shouldn't need anything else in subprocess, or this module failed.
 """
 
 from __future__ import with_statement
@@ skipping 215 matching lines @@
 
 
 def capture(args, **kwargs):
   """Captures stdout of a process call and returns it.
 
   Returns stdout.
 
   - Discards returncode.
   - Discards stderr. By default sets stderr=STDOUT.
   """
+  if kwargs.get('stdout') is None:
+    kwargs['stdout'] = PIPE
   if kwargs.get('stderr') is None:
     kwargs['stderr'] = STDOUT
-  return call(args, stdout=PIPE, **kwargs)[0][0]
+  return call(args, **kwargs)[0][0]
 
 
 def check_output(args, **kwargs):
   """Captures stdout of a process call and returns it.
 
   Returns stdout.
 
   - Discards stderr. By default sets stderr=STDOUT.
   - Throws if return code is not 0.
   - Works even prior to python 2.7.
   """
+  if kwargs.get('stdout') is None:
+    kwargs['stdout'] = PIPE
   if kwargs.get('stderr') is None:
     kwargs['stderr'] = STDOUT
-  return check_call(args, stdout=PIPE, **kwargs)[0]
+  return check_call(args, **kwargs)[0]