@Test
public void invokeStartNegative() {

    FunctionTestUtil.assertResult(substringFunction.invoke("test", -1), "t");
    FunctionTestUtil.assertResult(substringFunction.invoke("test", -2), "st");
    FunctionTestUtil.assertResult(substringFunction.invoke("test", -4), "test");
    FunctionTestUtil.assertResult(substringFunction.invoke("test", -2, 1), "s");
    FunctionTestUtil.assertResult(substringFunction.invoke("test", -3, 2), "es");
}