Tag: Assert

In the last post, I briefly described how to automatically migrate your MSTest tests to XUnit by using the XUnitConverter utility. Of course, nothing is ever that simple; MSTest has some concepts that XUnit expresses very differently¹ like how to share code between tests whether that is setup, fixtures, cleanup, or data. Some of these concepts are implemented differently enough that automating the migration from one to the other would be very difficult if not impossible. However, some of it really is that simple. Before we look at the difficult examples, I thought it would be useful to illustrate how some of the simple concepts map from MSTest to XUnit using an example².

So, let's look at an MSTest example (contrived, of course):

[TestClass]
public class MyTests
{
    private MemoryStream _stream;

    [TestInitialize]
    public void Initialize()
    {
        _stream = new MemoryStream();
    }

    [TestCleanup]
    public void Cleanup()
    {
        _stream.Dispose();
    }

    [TestMethod]
    public void Test1()
    {
        //Arrange
        //Act
        //Assert
    }

    [TestMethod]
    public void Test2()
    {
        //Arrange
        //Act
        //Assert
    }
}

Clearly, I cheated by not actually making the tests do anything, but the content of the test methods is mostly irrelevant; you set some stuff up, you do something, and you assert a result–it's all the same regardless of the test framework. However, this is a simple example of a test class written for the MSTest framework. There are attributes to tell the framework that the class is a test class, which methods inside of it are test methods, and which methods should be called before and after each test. In this case, our test initialization creates a stream, which is then disposed of in the cleanup method; each test method would get sandwiched in the middle.

After converting to XUnit with the converter tool, the same class will look something like this:

public class MyTests : IDisposable
{
    private MemoryStream _stream;

    public MyTests()
    {
        _stream = new MemoryStream();
    }

    public void Dispose()
    {
        _stream.Dispose();
    }

    [Fact]
    public void Test1()
    {
        //Arrange
        //Act
        //Assert
    }

    [Fact]
    public void Test2()
    {
        //Arrange
        //Act
        //Assert
    }
}

There are a few things that happened.

1. The class no longer has an attribute. XUnit knows the class is a test class because it contains tests³.
2. The tests are decorated with a [Fact] attribute, which is equivalent to [TestMethod].
3. The [TestInitialize] and [TestCleanup] attributes are gone. Instead, the class constructor is used for test initialization and the Dispose method along with deriving from IDisposable indicates that there is test cleanup code.

Overall, I love how the XUnit syntax works with C# syntax and .NET idioms in declaring tests. Not only does this reduce the ceremony around defining tests by reducing the various decorators, but it also allows for cleaner coding practices. For example, we can now correctly mark our memory stream member variable as readonly.

private MemoryStream _stream;

By relying on C# syntax and standard interfaces in this way, the lifecycle of a test is clearer too; XUnit will construct and dispose the class for each test in the class, making it easy to see how each test will run. This idiomatic way of declaring tests allows for separation of concerns, keeping test classes light and focused. This will be illustrated when we later look at other concepts in MSTest like [ClassInitialize] and [ClassCleanup], TestContext, and [DeploymentItem], and how XUnit tackles the problems these concepts solved.

1. and for good reasons, IMHO [↩]
2. XUnit documentation has a handy table but I don't think it's as illustrative as it could be [↩]
3. why MSTest did not make assumptions like this, I do not know [↩]