public void TestGetListOfCustomersWithBirthdayToday() { var customerManagerMock = new Mock <ICustomerManager>(); customerManagerMock.Setup(m => m.GetAllCustomers()) .Returns(new List <Customer> { new Customer { DateOfBirth = new DateTime(2000, DateTime.Today.Month, DateTime.Today.Day) }, new Customer { DateOfBirth = new DateTime(2018, 8, 9) } }); var customerAPI = new CustomerAPI(customerManagerMock.Object, null, null); var result = customerAPI.GetListOfCustomersWithBirthdayToday(); Assert.AreEqual(1, result.Count()); }