An alternative approach to structuring your tests in XUnit

I typically write my unit tests using the AAA(Arrange-Act-Assert) pattern. This pattern splits a test in 3 sections:

• The Arrange section of a unit test method initializes objects and sets the value of the data that is passed to the method under test.
• The Act section invokes the method under test with the arranged parameters.
• The Assert section verifies that the action of the method under test behaves as expected.

Here is an example from one of my projects using XUnit:

	[Fact]
	public void GetAllCustomers_Returns_Multiple_Customers()
	{
	//Arrange
	var unitOfWorkFactory = _container.GetRequiredService<IUnitOfWorkFactory>();
	var repository = _container.GetRequiredService<CustomerRepository>();
	//Act
	using var uow = unitOfWorkFactory.Create();
	var customers = repository.GetAllCustomers();
	//Assert
	Assert.NotEmpty(customers);
	}

view raw XUnitTest.cs hosted with ❤ by GitHub

In the example above you can see that I include the 3 sections of the AAA pattern inside the test method itself.

Recently I was reading a blog post by Jeremy Miller where I noticed he was using a different approach to separate the 3 sections:

	public class when_the_account_is_overdrawn : IAsyncLifetime
	{
	private readonly Account theAccount = new Account
	{
	Balance = 1000,
	MinimumThreshold = 100,
	Id = Guid.NewGuid()
	};
	private readonly TestMessageContext theContext = new TestMessageContext();
	// I happen to like NSubstitute for mocking or dynamic stubs
	private readonly IDocumentSession theDocumentSession = Substitute.For<IDocumentSession>();
	public async Task InitializeAsync()
	{
	var command = new DebitAccount(theAccount.Id, 1200);
	await DebitAccountHandler.Handle(command, theAccount, theDocumentSession, theContext);
	}
	[Fact]
	public void the_account_balance_should_be_negative()
	{
	theAccount.Balance.ShouldBe(-200);
	}
	}

view raw when_the_account_is_overdrawn.cs hosted with ❤ by GitHub

In the example above, Jeremy is using the IAsyncLifetime feature of XUnit to split the 3 sections:

	public class when_xxx : IAsyncLifetime
	{
	//Add your arrange code here
	public async Task InitializeAsync()
	{
	//Add your act code here
	}
	[Fact]
	public void the_should_xxx()
	{
	//Add your assert code here
	}
	}

view raw whenasync.cs hosted with ❤ by GitHub

This also works when you don't need async logic by using the constructor and the regular IDisposable interface:

What I like about this approach is that you have less repetitive code as the same arrange and act code can be used for multiple asserts. It allows you to easily group your test by test scenario and bring them logically together in one test class.

And as a nice bonus, it also solves the problem of finding good names for your test classes!

	public class when_xxx : IDisposable
	{
	//Add your arrange code here
	public when_xxx()
	{
	//Add your act code here
	}
	[Fact]
	public void the_should_xxx()
	{
	//Add your assert code here
	}
	}

view raw when.cs hosted with ❤ by GitHub