Existing mock implementation already has that feature. Mock attributes can be limited with `spec` attribute.


>>> inner_m = Mock(spec=["method2"], **{"method2.return_value": 1})
>>> m = Mock(spec=["method1"], **{"method1.return_value": inner_m})
>>> 
>>> m.method1().method2()
1
>>> 
>>> m.method1().attr
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.5/unittest/mock.py", line 580, in __getattr__
    raise AttributeError("Mock object has no attribute %r" % name)
AttributeError: Mock object has no attribute 'attr'