Trying to set an expectation on unsupported method messes up Mockito internal state.

[yanok]

Currently if one generates mocks with

@GenerateMocks(customMocks: MockSpec<Foo>(unsupportedMembers: {#m})

and then trying to set an expectation on foo.m, not only the test trying to do this fails (which is expected), but also all the following tests, since unsupported method throws without cleaning _storedArgs/_storedNamedArgs and that messes up Mockito internal state.

[iinozemtsev]

It's broader than this, internal state is also messed if thenReturn doesn't succeed:
when(mock).thenReturn(null!)

Probably no easy fix in mockito for this, but maybe an error message can be improved with possible explanations

[yanok]

Could be potentially fixed with #684. Actually I think we could get rid of internal state altogether.