public void DeleteCar_CantDeleteIfInUse() {
            Exception caugthException = null;
            var car = new Car {
                Id = 4,
                User = _currentUser
            };
            _fakeApplicationDbContext.Cars.Add(car);
            _fakeApplicationDbContext.Trips.Add(new Trip { Id = 1, User = _currentUser, Car = car });
            var carService = new CarService(_fakeApplicationDbContext, _mockCurrentUserService.Object);

            // Act
            bool deleted = false;
            try {
                deleted = carService.DeleteCar(car.Id);
            } catch (DbEntityValidationException ex) {
                caugthException = ex;
            }

            // Assert
            Assert.IsFalse(deleted);
            Assert.IsNotNull(caugthException);
        }
        public void DeleteCar_CanDelete() {
            const int carId = 2;
            _fakeApplicationDbContext.Cars.Add(new Car { Id = 1, User = _currentUser });
            _fakeApplicationDbContext.Cars.Add(new Car { Id = 2, User = _currentUser });
            _fakeApplicationDbContext.Cars.Add(new Car { Id = 3, User = _currentUser });
            _fakeApplicationDbContext.Cars.Add(new Car { Id = 4, User = _otherUser });
            _fakeApplicationDbContext.Cars.Add(new Car { Id = 5, User = _currentUser });
            var carService = new CarService(_fakeApplicationDbContext, _mockCurrentUserService.Object);

            // Act
            var deleted = carService.DeleteCar(carId);

            // Assert
            Assert.IsTrue(deleted);
        }