public static CustomerRegistry MakeExample () {
			var registry = new CustomerRegistry();
			registry.customers.Add(Customer.MakeExample());
			return registry;
		}
			[Theory] public static void Invariants (CustomerRegistry registry) {
				Assume.That(registry != null);
				// ReSharper disable once PossibleNullReferenceException
				registry.AssertInvariants();
			}