PHPUnit模拟对象和方法类型提示

I'm trying to create a mock object of \SplObserver using PHPunit and attach the mocked object to an \SplSubject. When I try to attach the mocked object to a class that implements \SplSubject, I get a catchable fatal error saying that the mocked object doesn't implement \SplObserver:I'm trying to create a mock object of \SplObser