I always love reading John Taylor's testimony of the Prophet Joseph Smith. And I'm grateful that I have a testimony as well. Mine came during a seminary class when we watched "The First Vision" movie. If you have a copy of the Church History Collection dvd, you can watch it too.
It's #3 - The First Vision. This is the original video dramatization of the events that led Joseph Smith to pray in the Sacred Grove, where he received the First Vision. This video can be used to teach the importance of obtaining and sharing a testimony of the First Vision. (14:42)