Make spy a context manager

Capture return value

NOTE: already implemented in 1.11

class SomeClass:
    def method(self, a):
        return a * 2

    def facade(self):
        self.method(4)
        return 'Done'


def test_some_class(mocker):
    spy = mocker.spy(SomeClass, 'method')
    o = SomeClass()
    o.facade()
    assert spy.called
    assert spy.call_count == 1

    print(spy.mock_calls[0])
    # nicely outputs method arguments
    # call(<m.SomeClass object at 0x7febfed74518>, 4)

    print(spy.return_value)
    # just tells us we have mock object here
    # <MagicMock name='method()' id='140651569552856'>
    
    # it would be much better to have there
    # assert spy.return_value == 8
    # or, rather
    # assert spy.mock_calls[0].return_value == 8

Spy as context manager

That's probably kind of misusing mocker object, but in my case there's a quite long test and I want to restrict fragment of code where particular spy object is applied.

def test_context_mgr(mocker):
    o = SomeClass()
    with mocker.spy(SomeClass, 'method') as spy:  # AttributeError: __enter__ here
        o.facade()
        assert spy.call_count == 1
    o.facade()

Currently I can only find arguments

The issue names no implementation file or test; start by reading the spy entry point and existing spy tests, then compare them with the context-manager example. Done means the spy can be used in a with block for the selected code fragment and the example's call-count assertions remain valid after exiting it.