And what is the test to know if a prophet is a real prophet or not?
As we are, as you state, commanded by God to do?
1 John 4
1Dear friends, do not believe every spirit, but test the spirits to see whether they are from God, because many false prophets have gone out into the world
1 John 41 BELOVED, believe not every spirit, but try the spirits whether they are of God: because many false prophets are gone out into the world.
2 Hereby know ye the Spirit of God: Every spirit that confesseth that Jesus Christ is come in the flesh is of God:
So, did Joseph Smith "confess... that Jesus Christ is come in the flesh"?
I saw two Personages, whose brightness and glory defy all description, standing above me in the air. One of them spake unto me, calling me by name and said, pointing to the other—This is My Beloved Son. Hear Him!" - Joseph Smith, Jr....and again
Doctrine and Covenants 1101 THE veil was taken from our minds, and the eyes of our understanding were opened.
2 We saw the Lord standing upon the breastwork of the pulpit, before us; and under his feet was a paved work of pure gold, in color like amber.
3 His eyes were as a flame of fire; the hair of his head was white like the pure snow; his countenance shone above the brightness of the sun; and his voice was as the sound of the rushing of great waters, even the voice of Jehovah, saying:
4 I am the first and the last; I am he who liveth, I am he who was slain; I am your advocate with the Father.