Simulators are mostly shared with the entire league, while some teams have their own 'internal' simulator, Currently, there are two simulators in the league. We always use the one from ER-Force, https://github.com/robotics-erlangen/framework. This simulator also has a realism settings, and has some useful features, like hiding the ball when it's blocked by a robot from the camera perspective. While testing in the simulator can get you quite far, you should always try to test on the field with control/mechanics, as the front assembly and the control of the robot can be quite different in reality and simulator. Testing tactics ect in the simulator should be fine.