public void TokenSystemDbService_GetCustomerById_ReturnsSingleCustomerSuccess() { // Arrange var mockContainer = new Mock <Container>(); var mockCosmosClient = new Mock <CosmosClient>(); var responseMock = new Mock <ItemResponse <Customer> >(); var existingCusotmers = new List <Customer> { new Customer { Id = "1111-11-111", FirstName = "First", Surname = "SecondName", Age = 35, CustomerType = CustomerType.AccountHolder, AccountNumber = 123456, Token = new Token { ServiceType = ServiceType.Transaction, TokenNumber = 1, Counter = 0, Status = Status.InQueue } }, new Customer { Id = "2222-222-222", FirstName = "Second", Surname = "Customer", Age = 35, CustomerType = CustomerType.Guest, SocialNumber = 76543, Token = new Token { ServiceType = ServiceType.Service, TokenNumber = 2, Counter = 0, Status = Status.InQueue } } }.AsQueryable(); mockContainer.Setup(x => x.GetItemLinqQueryable <Customer>(true, null, null)) .Returns((IOrderedQueryable <Customer>)existingCusotmers); mockCosmosClient.Setup(x => x.GetContainer(It.IsAny <string>(), It.IsAny <string>())) .Returns(mockContainer.Object); var serviceUnderTest = new TokenSystemDbService(mockCosmosClient.Object, It.IsAny <string>(), It.IsAny <string>()); // Act var response = serviceUnderTest.GetCustomerById(existingCusotmers.Last().Id); // Assert Assert.AreEqual(existingCusotmers.Last(), response); }