':func:`validate_signature_against_kwargs` raises an
``InvalidSignature`` exception if a function that has one mandatory
argument is not specified, and the missing optional arguments are
included in the exception.'

def test_mixed_missing_mandatory_failure(self):

    self.assertThat((lambda : validate_signature_against_kwargs(_mixed_arguments_function, set(['two', 'four']))), _raises_invalid_signature(missing_arguments=set(['one']), missing_optional_arguments=set(['three'])))
