拆解pytest中的单例类

Question

我有一个我在应用程序中使用的单例类（Singleton在元类中实现）

class Singleton(type):
    def __init__(self, *args, **kwargs):
        self.__instance = None
        super(Singleton, self).__init__(*args, **kwargs)

    def __call__(self, *args, **kwargs):
        if self.__instance is None:
            self.__instance = super(Singleton, self).__call__(*args, **kwargs)
            return self.__instance
        else:
            return self.__instance


class ApplicationContext(object):
    __metaclass__ = Singleton

    def __init__(self, db):
        pass

现在我希望这个对象位于py.test上下文中 - 但我希望它在某些测试中不受影响。 我试图创建一个拆卸功能，但它似乎没有工作......

@pytest.fixture
def context(db, request):
    _context = ApplicationContext(db)

    def teardown():
        print 'teardown'
        del _context   #this is not working. What should be done here?

    request.addfinalizer(teardown)
    return _context