'Test that we don\'t re-write files that we haven\'t changed'

def test_dirty(self):

    self.conf1.set('a', 'b')
    self.conf1.write()
    with open(self.path1, 'w') as f:
        f.write('canary')
    self.conf1.write()
    with open(self.path1) as f:
        self.assertEqual('canary', f.read())
