public async Task DeleteById(Pizza p)
{
await Pizzas.Add(p);
await Pizzas.Delete(p.Id);
Assert.Empty(await Pizzas.GetAll());
var toppings = (await Toppings.GetAll()).ToList();
Assert.Equal(p.Toppings.Count, toppings.Count);
Assert.All(toppings, t => Assert.Contains(t, p.Toppings));
}