public void AddBillTest()
{
Assert.AreEqual(0, dataService.GetAllBills().Count());
dataService.AddCar("Skoda", "Fabia", "Style", 210, "Silver Metalic", VehicleType.Small_car, FuelType.Petrol, Transmission.Manual);
dataService.AddWarehouseItem(dataService.GetAllCars().First(), 10000);
dataService.AddBill(dataService.GetAllWarehouseItems().First());
Assert.AreEqual(1, dataService.GetAllCars().Count());
}