Biblical Test of truth tellers

Do you know one of the Biblical test that defines real believers from false teachers.
Look at 1 John 4:1 - 6 - it gives us the test -- If someone is trying to tell you about Godly matters - TYhe question you need to ask is " Do you believe Jesus Christ came in the flesh--in short HE WAS FULLY GOD AND FULLY MAN. Many do not yet talk about Jesus as if they do. Many deny His deity , others see Him as a great moral teacher. As Christians we must place Him as God / man and keep 1 John 4: 1-6 in mind.