public FEELFnResult<String> invoke(@ParameterName("string") String string, @ParameterName("start position") Number start) {
        return invoke(string, start, null);
    }
@Test
    void invokeLengthOutOfListBounds() {
        FunctionTestUtil.assertResult(substringFunction.invoke("test", 2, 3), "est");
        FunctionTestUtil.assertResult(substringFunction.invoke("test", -3, 3), "est");
    }