python mox example with subprocess.Popen and builtin open

example.py

#!/usr/bin/env python
from subprocess import *

class Example(object):
    def run(self):
        a = open("/etc/example.txt").read()
        b = Popen("/usr/bin/example.sh", shell=True, stdout=PIPE).communicate()[0]
        return a + b

if __name__ == "__main__":
    Example().run()

test.py

import unittest
from mox import Mox
from StringIO import StringIO
from subprocess import *
import __builtin__

import example

txt = '''
aaaa
'''.lstrip()

shout = '''
bbbb
'''.lstrip()

expect = '''
aaaa
bbbb
'''.lstrip()

class MockPopen(object):
    def __init__(self, stdout):
        self.stdout = stdout

    def communicate(self):
        return [self.stdout]

class TestExample(unittest.TestCase):
    def test_run(self):
        m = Mox()

        m.StubOutWithMock(__builtin__, 'open')
        open("/etc/example.txt").AndReturn(StringIO(txt))

        m.StubOutWithMock(example, "Popen")
        example.Popen("/usr/bin/example.sh", shell=True, stdout=PIPE).AndReturn(MockPopen(shout))

        m.ReplayAll()
        e = example.Example()
        result = e.run()
        m.VerifyAll()
        m.UnsetStubs()

        self.assertEqual(result, expect)

if __name__ == "__main__":
    unittest.main()