def test_grammar_typechecking(self):

        grammar_types = [('data', [str]), ('transform', [list])]
        assert_grammar_typechecking(grammar_types, MarkRef())
Throw a custom error from a handler method and catch (and format) it 
dataset/ETHPy150Open wrobstory/vincent/tests/test_vega.py/TestMarkRef.test_grammar_typechecking--crossover with--dataset/ETHPy150Open dgraziotin/dycapo/piston/tests.py/ErrorHandlerTest.test_customized_error_handler