Test film is like a practice run for making a real movie. Just like how you might practice drawing a picture before making the final one, movie makers make a test film first to make sure everything will be perfect in the real movie. They use the test film to see how the characters move and talk, how the camera angles look, and what the special effects will look like. It's like a trial run to make sure everything will be just right when they make the real movie that we get to watch in theaters or on TV.