mocking - How to mock a base class with python mock library

Question

I try to use mock to write some unit-tests in python.

For example I have the following class:

class TCPHandler(socketserver.BaseRequestHandler):
    def handle(self):
        self.data = self.request.recv(1024).strip()

And I only want to test the handle method. Without having to assume anything about socketserver.BaseRequestHandler. I for example want to assert that handle calls recv with the argument 1024. Is it possible to do such thing with mock? I.e. replacing the base class socketserver.BaseRequestHandler with a mock? Or am I off track with that idea?

---

With the answer of ecatmur (thank you!) I first tried the following:

patcher = patch.object(TCPHandler, '__bases__', (Mock,))
with patcher:
    patcher.is_local = True
    handler = TCPHandler()
    handler.handle()

But now handle is not called anylonger and dir(handler) gives:

['assert_any_call', 'assert_called_once_with', 'assert_called_with', 'assert_has_calls', 'attach_mock', 'call_args', 'call_args_list', 'call_count', 'called', 'configure_mock', 'method_calls', 'mock_add_spec', 'mock_calls', 'reset_mock', 'return_value', 'side_effect']

type(handler) gives <class 'mock.TCPHandler'>

Which I interpret that patching the base class also turns my derived class into a mock.

---

I now gave another idea a try:

mock = MagicMock()
TCPHandler.handle(mock)
#assertions

However the mock seems not to be called.

Answer 1

You can do this by patching the derived class's __bases__:

def test_derived():
    patcher = mock.patch.object(Derived, '__bases__', (mock.Mock,))
    with patcher:
        patcher.is_local = True
        d = Derived()
        print d.foo()

The is_local hack is necessary to stop mock.patch from trying to call delattr when reversing the patch.