Use context manager to manage OS environment in tests

test/cflags/gyptest-cflags.py

 #!/usr/bin/env python
 
 # Copyright (c) 2012 Google Inc. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """
-Verifies build of an executable with C++ define specified by a gyp define, and
-the use of the environment during regeneration when the gyp file changes.
+Verifies the use of the environment during regeneration when the gyp file
+changes, specifically via build of an executable with C preprocessor
+definition specified by CFLAGS.
+
+In this test, gyp and build both run in same local environment.
 """
 
-import os
-import sys
 import TestGyp
 
-env_stack = []
+# CPPFLAGS works in ninja but not make; CFLAGS works in both
+FORMATS = ('make', 'ninja')
 
+test = TestGyp.TestGyp(formats=FORMATS)
 
-def PushEnv():
-  env_copy = os.environ.copy()
-  env_stack.append(env_copy)
-
-def PopEnv():
-  os.environ.clear()
-  os.environ.update(env_stack.pop())
-
-formats = ['make', 'ninja']
-
-test = TestGyp.TestGyp(formats=formats)
-
-try:
-  PushEnv()
-  os.environ['CFLAGS'] = ''
-  os.environ['GYP_CROSSCOMPILE'] = '1'
+# First set CFLAGS to blank in case the platform doesn't support unsetenv.
+with TestGyp.LocalEnv({'CFLAGS': '',
+                       'GYP_CROSSCOMPILE': '1'}):
   test.run_gyp('cflags.gyp')
   test.build('cflags.gyp')
-finally:
-  # We clear the environ after calling gyp.  When the auto-regeneration happens,
-  # the same define should be reused anyway.  Reset to empty string first in
-  # case the platform doesn't support unsetenv.
-  PopEnv()
-
 
 expect = """FOO not defined\n"""
 test.run_built_executable('cflags', stdout=expect)
 test.run_built_executable('cflags_host', stdout=expect)
 
 test.sleep()
 
-try:
-  PushEnv()
-  os.environ['CFLAGS'] = '-DFOO=1'
-  os.environ['GYP_CROSSCOMPILE'] = '1'
+with TestGyp.LocalEnv({'CFLAGS': '-DFOO=1',
+                       'GYP_CROSSCOMPILE': '1'}):
   test.run_gyp('cflags.gyp')
   test.build('cflags.gyp')
-finally:
-  # We clear the environ after calling gyp.  When the auto-regeneration happens,
-  # the same define should be reused anyway.  Reset to empty string first in
-  # case the platform doesn't support unsetenv.
-  PopEnv()
-
 
 expect = """FOO defined\n"""
 test.run_built_executable('cflags', stdout=expect)
 
 # Environment variables shouldn't influence the flags for the host.
 expect = """FOO not defined\n"""
 test.run_built_executable('cflags_host', stdout=expect)
 
 test.sleep()
 
-try:
-  PushEnv()
-  os.environ['CFLAGS'] = ''
+with TestGyp.LocalEnv({'CFLAGS': ''}):
   test.run_gyp('cflags.gyp')
   test.build('cflags.gyp')
-finally:
-  # We clear the environ after calling gyp.  When the auto-regeneration happens,
-  # the same define should be reused anyway.  Reset to empty string first in
-  # case the platform doesn't support unsetenv.
-  PopEnv()
-
 
 expect = """FOO not defined\n"""
 test.run_built_executable('cflags', stdout=expect)
 
 test.sleep()
 
-try:
-  PushEnv()
-  os.environ['CFLAGS'] = '-DFOO=1'
+with TestGyp.LocalEnv({'CFLAGS': '-DFOO=1'}):
   test.run_gyp('cflags.gyp')
   test.build('cflags.gyp')
-finally:
-  # We clear the environ after calling gyp.  When the auto-regeneration happens,
-  # the same define should be reused anyway.  Reset to empty string first in
-  # case the platform doesn't support unsetenv.
-  PopEnv()
-
 
 expect = """FOO defined\n"""
 test.run_built_executable('cflags', stdout=expect)
 
 test.pass_test()