public void TestGetCountbyGenderSuccess() { var personList = new List <Person> { new Person { Name = "George", Gender = "Male" } }; _addressBookLoader.Setup(c => c.LoadAddressBook()).Returns(personList); classUnderTest = new AddressBookService(_addressBookLoader.Object, _logger.Object); var result = classUnderTest.GetCountbyGender("Male"); Assert.Equal(1, result.Result); }