public void DoesRegistrationNumberExistTest()
        {
            var garageHandler = new Uppgift5_Ludvig_Baummann_Olsson.GarageHandler();

            garageHandler.CreateGarage(1);
            Assert.IsTrue(garageHandler.AddVehicle(new Uppgift5_Ludvig_Baummann_Olsson.Vehicle("ABC123", "Red", 4)));
            Assert.IsTrue(garageHandler.DoesRegistrationNumberExist("ABC123"));
        }