':func:`validate_signature_against_kwargs` raises an
``InvalidSignature`` exception if a function has one argument with a
default, and a single wrong argument is passed in.'

def test_default_wrong_arg_failure(self):

    self.assertThat((lambda : validate_signature_against_kwargs(_one_default_argument_function, set(['unexpected']))), _raises_invalid_signature(unexpected_arguments=set(['unexpected']), missing_optional_arguments=set(['arg'])))
