The test of Mt Sinai is about hearing from God first-hand.
Exodus 20:18-20 When the people saw the thunder and lightning and heard the trumpet and saw the mountain in smoke, they trembled with fear. They stayed at a distance and said to Moses, 'Speak to us yourself and we will listen. But do not have God speak to us or we will die'. Moses said to the people, 'Do not be afraid.God has come to test you, so that the fear of God will be with you to keep you from sinning'.