Dressage tests in horse shows ask the rider to demonstrate essential control over the horse by showing accuracy for riding in a circle and in a straight line. Practice riding in a straight line and changing directions with a horse to prepare for a dressage test with help from an equestrian team head coach in this video on horse show preparation.
Every dressage test asks the rider to do a variety of different things depending on the level of test. At the most simple test, it simply asks you to demonstrate essential control over your horse and asks you to demonstrate accuracy as far as your circle and the place of execution of your aids. The most basic test will always have you start with a straight line on the center line. Usually you'll halt at X, which is the middle of the ring. And it's a good basic thing to practice if you're at home. Just riding a nice straight line. Usually a dressage test will ask you to ride circles that are even both directions and they'll always have you make a change of direction which makes you test your horses flexibility and equality in each direction.
Specialty: Hunter, Jumper, Equitation