MS Unit testing example

Question

I'm struggling to get my head around unit testing. I've been following examples from both Nerd dinner and pro asp.net MVC framework, but as soon as I attempt my own quickly become stuck. As a test I have tried to build a validation class that simply using login information - usename and password to return a user from a repository. I've used this example as it's pretty simple to imagine what tests one might perform: Is_Password_Valid, Is_Username_Valid etc.

I've spent far too long trying to get my noggin around this. Could any one provide an example of how they might approach this as a unit test? I think once I've cracked this I'll be away.

//Arrange
string email = "[email protected]";
string password = "test";

//Arrange
List<Customer> customer = new List<Customer>();

customer.Add(new Customer { CustomerId = 1, Email = email, Password = "best", FirstName = "test", LastName = "wods", Sex = true });
mockRepos = new Moq.Mock<ICustomerRepository>();
mockRepos.Setup(x => x.GetCustomerByPasswordUsername(email, password)).Returns(customer.First());
Authenticate auth = new Authenticate(mockRepos.Object);

//Act
var result = auth.Login(email, password);

//Assert
//this is where I start to become unstuck??????

Answer 1

It definitely looks like you are on the right track, but let me try to explain how I would go about the test.

The actual system under test (SUT) here is the Authenticate class. You have not told a lot about it, so I will assume the following:

It uses an instance of ICustomerRepository to determine the existence of a user based on a combination of username (email) and password.

When the repostiory returns an instance of Customer, given a username and password combination, the Login method returns true. When the repository returns null, the Login method returns false.

I will use these assumptions in the following, but if they are not correct, I´m sure you will be able to change the tests so that they make sense for your scenario.

Test 1: When the username/password combination is correct, Login will return true

public void LoginWillReturnTrueForAValidUsernamePasswordCombination()
{
    string email = "[email protected]";
    string password = "test";

    //Dummy customer
    var customer = new Customer();

    //Create mock
    var mockRepos = new Moq.Mock<ICustomerRepository>();
    mockRepos.Setup(x => x.GetCustomerByPasswordUsername(
            It.Is<string>(s => s == email), 
            It.Is<string>(s => s == password))
        .Returns(customer);

    var auth = new Authenticate(mockRepos.Object);

    //Act
    var result = auth.Login(email, password);

    //Assert
    Assert.IsTrue(result);
}

Note the use of It.Is. Basically, the mock is set up in a way that it will only return the dummy customer object when the email and password defined in your test are passed to the GetCustomerByPasswordUsername method.

Test 2: When the username/password combination is incorrect, Login will return false

public void LoginWillReturnFalseForAnInvalidUsernamePasswordCombination()
{
    string email = "[email protected]";
    string password = "test";

    //Create mock
    var mockRepos = new Moq.Mock<ICustomerRepository>();
    mockRepos.Setup(x => x.GetCustomerByPasswordUsername(
            It.Is<string>(s => s == email), 
            It.Is<string>(s => s == password))
        .Returns<Customer>(null);

    var auth = new Authenticate(mockRepos.Object);

    //Act
    var result = auth.Login(email, password);

    //Assert
    Assert.IsFalse(result);
}

Although implicitly tested by the above tests, you may want to go a step further and write a test that ensures that the Login method passes the right parameters to the repository. Such a test could look like the following:

Test 3: Login will invoke repository correctly

public void LoginWillInvokeGetCustomerByPasswordUsernameCorrectly()
{
    string email = "[email protected]";
    string password = "test";

    //Create mock
    var mockRepos = new Moq.Mock<ICustomerRepository>();
    mockRepos.Setup(x => x.GetCustomerByPasswordUsername(
            It.Is<string>(s => s == email), 
            It.Is<string>(s => s == password))
        .Returns<Customer>(null)
        .Verifiable();

    var auth = new Authenticate(mockRepos.Object);

    //Act (ignore result. We are only testing correct invocation)
    auth.Login(email, password);

    //Assert
    mockRepos.Verify();
}

The Verify method of a mock throws an exception if the methods that have been setup have not been called.

I hope this helps. Don't hesitate to ask if you have further questions.