How to write good unit tests? Avoid these two issues

These days, I needed to update some tests. I found two 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 in your tests. 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 readable, even more 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 threw 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 = "[e-mail]",
            SupportEmail = "[e-mail]"
        });

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

    return Task.CompletedTask;
}

The tests used Moq, a mocking library for .NET. I already wrote about the things I like and dislike about Moq. Let's see the two issues in our sample test.

Can you spot any other issues? The naming convention isn't one.

Photo by Drew Patrick Miller on Unsplash

Reduce the noise

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

Use builder methods to reduce complex setup scenarios.

Let's reduce the noise from our example 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 = "[e-mail]",
            SupportEmail = "[e-mail]"
        });

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

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.

Make your test values obvious

In our example, the test name says 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 your scenario under test and test value 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.

[TestMethod]
public void AccountController_SenderEmailIsNull_ThrowsException()
{
    var emailConfig = new Mock<IOptions<EmailConfiguration>>();
    emailConfig.SetupGet(options => options.Value)
        .Returns(new EmailConfiguration
        {
            SenderEmail = null,
            ReplyToEmail = "[e-mail]",
            SupportEmail = "[e-mail]"
        });

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

Finally, as an aside, we don't need a mock on IOptions<EmailConfiguration>. We can use the Option.Create method instead. Let's do it.

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

    Assert.ThrowsException<ArgumentNullException>(() =>
        CreateAccountController(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.

Upgrade your unit testing skills with my course: Mastering C# Unit Testing with Real-world Examples on my Gumroad page. Practice with hands-on exercises and learn best practices by refactoring real-world unit tests.

Happy unit testing!