private GravityState gravityState;
protected void setUp() throws Exception {
super.setUp();
UniverseStateFactory universeStateFactory = new UniverseStateFactory();
UniverseState universeState = universeStateFactory.createRandomUniverseState();
universe = new BasicUniverse(universeState);
GravityStateFactory gravityStateFactory = new GravityStateFactory();
gravityState = gravityStateFactory.createGravityState();
}