public async Task AddBeerWholesaler_BeerNotExist()
        {
            var command = new AddBeerToWholesalerCommand {
                BeerId = 100, WholesalerId = 1, Stock = 20
            };

            using (var context = new BeerContext(ContextOptions))
            {
                var service = new WholesalerService(context);

                await Assert.ThrowsAsync <CustomBadRequestException>(() => service.AddBeer(command));
            }
        }
        public async Task AddBeerWholesaler_ReturnOk()
        {
            var command = new AddBeerToWholesalerCommand {
                BeerId = 5, WholesalerId = 2, Stock = 20
            };

            using (var context = new BeerContext(ContextOptions))
            {
                var service = new WholesalerService(context);

                await service.AddBeer(command);

                var wholesaler = await context.Wholesalers
                                 .Include(w => w.WholesalerBeers)
                                 .SingleOrDefaultAsync(w => w.Id == command.WholesalerId);

                Assert.Contains(wholesaler.WholesalerBeers, wb => wb.BeerId == 5);
            }
        }