In which cases is it imperative to test the brakes?

Your answer is correct because in German traffic rules, it is essential to test the brakes in certain situations to ensure safety. Specifically, you must test the brakes when driving a different vehicle since you may not be familiar with its braking behavior. Also, if a vehicle has not been used for a longer period, the brakes might have become less effective due to rust or other factors, so testing them is crucial. However, testing the brakes is not required each time the engine oil is changed, as the oil change does not directly affect brake performance. Remembering these key points helps ensure safe driving conditions.