Fix to replace current env with a blank one.

gmerge_test.py

 #!/usr/bin/python
 
 # Copyright (c) 2011 The Chromium OS 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 gmerge."""
 
 import gmerge
 import os
@@ skipping 12 matching lines @@
         'CHROMEOS_RELEASE_BOARD=x86-mario\r\n',
         'CHROMEOS_DEVSERVER=http://localhost:8080/\n']
 
   def testLsbRelease(self):
     merger = gmerge.GMerger(self.lsb_release_lines)
     self.assertEqual({'CHROMEOS_RELEASE_BOARD': 'x86-mario',
                       'CHROMEOS_DEVSERVER': 'http://localhost:8080/'},
                      merger.lsb_release)
 
   def testPostData(self):
-    original_use = os.environ.get('USE', '')
+    old_env = os.environ
+    os.environ = {}
     os.environ['USE'] = 'a b c d +e'
     gmerge.FLAGS = Flags({'accept_stable': 'blah'})
 
     merger = gmerge.GMerger(self.lsb_release_lines)
     self.assertEqual(
         'use=a+b+c+d+%2Be&pkg=package_name&board=x86-mario&accept_stable=blah',
         merger.GeneratePackageRequest('package_name'))
-    os.environ['USE'] = original_use
+    os.environ = old_env
 
 
 if __name__ == '__main__':
   unittest.main()