public void PopularBookTest() { var bookManagerMock = new Mock <IBookManager>(); var customerManagerMock = new Mock <ICustomerManager>(); customerManagerMock.Setup(m => m.GetPopularBookList(It.IsAny <int>())) .Returns(new PopularBookList { PopularBook = new List <PopularBook>() }); var customerAPI = new CustomerAPI(customerManagerMock.Object); var successfull = customerAPI.PopularStatus(1, 23); Assert.AreEqual(BookReturnStatus.OK, successfull); customerManagerMock.Verify(m => m.AddCustomer(It.IsAny <int>()), Times.Once); }