Deuteronomy 13:1-5,"If a prophet, or one who foretells by dreams, appears among you and announces to you a miraculous sign or wonder, and if the sign or wonder of which he has spoken takes place, and he says, "Let us follow other gods" (gods you have not known) "and let us worship them,"you must not listen to the words of that prophet or dreamer. The LORD your God is testing you to find out whether you love him with all your heart and with all your soul. It is the LORD your God you must follow, and him you must revere. Keep his commands and obey him; serve him and hold fast to him. That prophet or dreamer must be put to death, because he preached rebellion against the LORD your God, who brought you out of Egypt and redeemed you from the land of slavery; he has tried to turn you from the way the LORD your God commanded you to follow. You must purge the evil from among you."

Deuteronomy 18:20-22,"But a prophet who presumes to speak in my name anything I have not commanded him to say, or a prophet who speaks in the name of other gods, must be put to death." You may say to yourselves, "How can we know when a message has not been spoken by the LORD ?" If what a prophet proclaims in the name of the LORD does not take place or come true, that is a message the LORD has not spoken. That prophet has spoken presumptuously. Do not be afraid of him."

1 John 4:1,"Dear friends, do not believe every spirit, but test the spirits to determine if they are from God, because many false prophets have gone out into the world."

How to test:

1. Do they ever give false prophecies? Does 100% of their predictions of future events come true? -Deuteronomy 18:21-22
2. Do they contact departed spirits? - Deuteronomy 18:11
3. Do they use means of divination? - Deuteronomy 18:11
4. Do they involve mediums or witches? - Deuteronomy 18:11
5. Do they follow false gods or idols? - Exodus 20:3-4; Deuteronomy 13:1-3
6. Do they deny the deity of Jesus Christ? - Colossians 2:8-9
7. Do they deny the humanity of Jesus Christ? - 1 John 4:1-2
8. Do their prophecies shift focus off of Jesus Christ? - Revelation 19:10
9. Do they advocate abstaining from certain foods and meats for spiritual reasons? - 1 Timothy 4:3-4
10. Do they deprecate or deny the need for marriage? - 1 Timothy 4:3
11. Do they promote immorality? - Jude verse 4 and 7
12. Do they encourage legalistic self-denial? - Colossians 2:16-2

A positive answer to any of these questions means that the prophet is not speaking for God.