Two issues to avoid to write good unit tests

How to write good unit tests: Two issues to avoid

These days, I needed to update some unit tests. I found two types of issues on them. Please, continue to read. Maybe, you’re a victim of those issues, too.

To write good unit tests, avoid complex setup scenarios and hidden test values. Often tests are bloated with unneeded or complex code in the Arrange part and full of magic or hidden test values. Unit tests should be even more readable than production code.

The tests

The tests I needed to update were for an ASP.NET Core API controller, AccountController. This controller created, updated and suspended user accounts. Also, it sent a welcome email to new users.

These tests checked a configuration object for the sender, reply-to and contact-us email addresses. The welcome email contained those three emails. If the configuration files miss one of the email addresses, the controller throws an exception from its constructor.

Let’s see one of the tests. This test checks for the sender email.

[TestMethod]
public Task AccountController_SenderEmailIsNull_ThrowsException()
{
    var mapper = new Mock<IMapper>();
    var logger = new Mock<ILogger<AccountController>>();
    var accountService = new Mock<IAccountService>();
    var accountPersonService = new Mock<IAccountPersonService>();
    var emailService = new Mock<IEmailService>();
    var emailConfig = new Mock<IOptions<EmailConfiguration>>();
    var httpContextAccessor = new Mock<IHttpContextAccessor>();

    emailConfig.SetupGet(options => options.Value)
        .Returns(new EmailConfiguration()
        {
            ReplyToEmail = "email@email.com",
            SupportEmail = "email@email.com"
        });

    Assert.ThrowsException<ArgumentNullException>(() =>
        new AccountController(
            mapper.Object,
            logger.Object,
            accountService.Object,
            accountPersonService.Object,
            emailService.Object,
            emailConfig.Object,
            httpContextAccessor.Object
        ));

    return Task.CompletedTask;
}

This tests uses Moq to create stubs and mocks.

Can you spot any issues in our sample test? The naming convention isn’t one, by the way.

Let’s see the two issues to avoid to write good unit tests.

Adjusting dials on a mixer
Photo by Drew Patrick Miller on Unsplash

1. Reduce the noise

Our sample test only cares about one object, IOptions<EmailConfiguration>. All other objects are noise for the purpose of this test. They don’t have anything to do with the scenario under test.

Use builder methods to reduce complex setup scenarios.

Let’s reduce the noise from our test with a MakeAccountController() method. It will receive the only parameter the test needs.

After this change, our test looked like this:

[TestMethod]
public void AccountController_SenderEmailIsNull_ThrowsException()
{
    var emailConfig = new Mock<IOptions<EmailConfiguration>>();
    emailConfig.SetupGet(options => options.Value)
        .Returns(new EmailConfiguration
        {
            ReplyToEmail = "email@email.com",
            SupportEmail = "email@email.com"
        });

    // Notice how we reduced the noise with a builder
    Assert.ThrowsException<ArgumentNullException>(() =>
        MakeAccountController(emailConfig.Object));
    
    // We don't neet a return statement here
}

private AccountController MakeAccountController(IOptions<EmailConfiguration> emailConfiguration)
{
    var mapper = new Mock<IMapper>();
    var logger = new Mock<ILogger<AccountController>>();
    var accountService = new Mock<IAccountService>();
    var accountPersonService = new Mock<IAccountPersonService>();
    var emailService = new Mock<IEmailService>();
    var emailConfig = new Mock<IOptions<EmailConfiguration>>();
    var httpContextAccessor = new Mock<IHttpContextAccessor>();

    return new AccountController(
            mapper.Object,
            logger.Object,
            accountService.Object,
            accountPersonService.Object,
            emailService.Object,
            emailConfiguration,
            httpContextAccessor.Object);
}

Also, since our test doesn’t have any asynchronous code, we could remove the return statement and turned our test into a void method.

With this refactor, our test started to look simpler and easier to read. Now, it’s clear this test only cares about the EmailConfiguration class.

2. Make your test values obvious

Our test states in its name that the sender email is null. Anyone reading this test would expect to see a variable set to null and passed around. But, that’s not the case.

Make scenarios under test and test values extremely obvious.

Please, don’t make developers to decode your tests.

To make the test scenario obvious in our example, let’s add SenderEmail = null to the intialization of the EmailConfiguration object.

[TestMethod]
public void AccountController_SenderEmailIsNull_ThrowsException()
{
    var emailConfig = new Mock<IOptions<EmailConfiguration>>();
    emailConfig.SetupGet(options => options.Value)
        .Returns(new EmailConfiguration
        {
            // The test value is obvious now
            SenderEmail = null,
            ReplyToEmail = "email@email.com",
            SupportEmail = "email@email.com"
        });

    Assert.ThrowsException<ArgumentNullException>(() =>
        MakeAccountController(emailConfig.Object));
}

If we have similar scenarios, we can use a constant like const string NoEmail = null. Or prefer object mothers and builders to create test data.

Don’t write mocks for IOptions

Finally, as an aside, we don’t need a mock on IOptions<EmailConfiguration>.

Don’t use a mock or a stub with the IOptions interface. That would introduce extra complexity. Use Options.Create() with the value to configure instead.

Let’s use the Option.Create() method instead.

[TestMethod]
public void AccountController_SenderEmailIsNull_ThrowsException()
{
    var emailConfig = Options.Create(new EmailConfiguration
    {
        SenderEmail = null,
        ReplyToEmail = "email@email.com",
        SupportEmail = "email@email.com"
    });

    Assert.ThrowsException<ArgumentNullException>(() =>
        MakeAccountController(emailConfig));
}

Voilà! That’s way easier to read. Do you have noise and hidden test values in your own tests? Remember, readability is one of the pillars of unit testing. Don’t make developers to decode your tests.

For other tips on writing unit tests, check my follow-up on writting failing tests first and my Unit Testing Best Practices. Also, check my takeaways from the book The Art of Unit Testing.

Happy unit testing!