public async Task CustomerIsAddedSuccessfully() { MockUnitOfWOrk.Setup(p => p.CustomerRepository.Create(It.IsAny <Customer>())) .Returns(() => TestCustomers[0]); MockUnitOfWOrk.Setup(m => m.SaveAsync()).ReturnsAsync(() => new List <Guid>() { TestCustomers[0].Id }.AsEnumerable()); var result = await SystemUnderTest.AddCustomerAsync(TestCustomers[0]); Assert.Equal(TestCustomers[0].Id, result); }