Migration – somewhat abstract

Running XUnit Tests, Using Traits, and Leveraging Parallelism

We have arrived at the end of this little series on migrating unit tests from MSTest to XUnit (specifically, XUnit 2). While earlier posts concentrated on writing the tests and the XUnit counterparts to MSTest concepts, this post will briefly look at some non-code aspects to XUnit; most importantly, we will look at getting the tests to run.

Do not depend on test order
One thing to watch out for after migrating your tests is the order in which tests are run. MSTest allowed us to abuse testing by assuming that tests would run in a specific order. XUnit does away with this and will run tests in a random order. This can help to find some obscure bugs, but it can also make migration a little tougher, especially when tests share a data store or some other test fixture. Watch out for that.

Visual Studio

Running tests inside Visual Studio is really simple. Following in the footsteps of web development trends, rather than requiring an extension to the development environment, XUnit uses package management¹. All you need to do is add the Visual Studio XUnit test runner package to your project and Visual Studio will be able to detect and run your XUnit tests just like your old MSTests.

Of course, if you're like me and absolutely loathe the built-in Visual Studio test explorer, you can use Resharper (or dotCover), which has built-in support for XUnit.

Command Line

More often than not, our continuous integration setups are scripted and we're unlikely to be running our unit tests via the development tool, such as Visual Studio. For situations like this, you can add the XUnit command line test runner package to your project. This provides a command line utility for running your tests with arguments to control exactly what tests and how².

Once the package has been added, you can browse to where Nuget is storing packages for your particular project. In the tools folder of the console runner package folder, you will find xunit.console.exe. If you run this with the -? argument, you will get some helpful information.

xunit.console.exe -?

The three options I use the most are -trait, -notrait, and -parallel.

Traits

The two trait options control what tests you are running based on metadata attached to those tests. This is really useful if you have some tests that are resource heavy and only used in certain circumstances, such as stress testing. In MSTest, you could attach arbitrary metadata onto test methods using the TestProperty attribute. XUnit provides a similar feature using Trait. For example, [Trait("Category", "ManualOnly")] could be used to put a method into the ManualOnly category. You could then use the following line to execute tests that lack this trait.

xunit.console.exe -notrait "Category=ManualOnly"

If you wanted to only run tests with a specific trait, you do the same thing but with -trait instead. Both of these options are very useful when combined with -parallel.

Parallelism

XUnit can run tests in parallel, but tests within the same collection are never run in parallel with each other. By default, each test class is its own collection. Test classes can be combined into collections using the Collection attribute. Tests within the same collection will be executed randomly, but never in parallel.

The -parallel option provides four options: no parallelism, running tests from different assemblies in parallel, running tests from different collections in parallel, or running tests from different assemblies and different collections in parallel.

The difference between assembly parallelism, collection parallelism, and both together

Let's assume you have two assemblies, A and B. Assembly A has three collections; 1, 2, and 3. Assembly B has three collections; 4, 5, and 6.

No Parallelism
-parallel none

XUnit will run each collection in one of the assemblies, one at a time, then run each collection in the other assembly one at a time.

Collections 1, 2, 3, 4, 5, and 6 will never execute at the same time as each other.

Parallel Assemblies
-parallel assemblies

XUnit will run each collection in assembly A, one at a time, at the same time as running each collection in assembly B, one at a time.

Collections 1, 2, and 3 will not execute at the same time as each other; Collections 4, 5, and 6 will not execute at the same time as each other; but collections 1, 2, and 3 will execute in parallel with 4, 5, and 6, as the 1, 2, and 3 are in a different assembly to 4, 5, and 6.

Parallel Collections
-parallel collections

XUnit will run each collection within an assembly in parallel, but only one assembly at a time.

Collections 1, 2 and 3 will execute parallel; collections 4, 5, and 6 will execute in parallel; but, 1, 2, and 3 will not run at the same time as 4, 5, and 6.

Parallel Everything
-parallel all

XUnit will run each collection in parallel, regardless of its assembly.

Collections 1, 2, 3, 4, 5, and 6 will run in parallel, each potentially running at the same time as any other.

Beware running tests in parallel when first migrating from MSTest. It is a surefire way of finding some heinous test fixture dependencies and you risk thinks like deadlocking on resources. Usually, running assemblies in parallel is a lot safer than running collections in parallel, assuming that tests are collocated in assemblies based on their purpose and the resources they interact with.

In Conclusion…

That brings us to the end of the series. I have focused primarily on migrating from MSTest, leaving out a lot of the nuances to XUnit. I highly recommend continuing your education with the XUnit documentation and through experimentation; having personally migrated several projects, I know you won't regret it.

I love this approach to augmenting the development environment. It requires no additional tooling setup to get your dev environment working. The source itself controls the tooling versions and installation. Wonderful [↩]
You can control how tests run under MSBuild too by using various properties. This is discussed more on the XUnit site [↩]

DataSource and Data-driven Testing Using XUnit

If you are anything like me, you avoided data-driven tests in MSTest because they were such a pain to write and maintain. However, I know not everyone is like me and I also know that even though we try to avoid things, we do not always succeed. So, in this entry in the series on migrating from MSTest to XUnit, we will look at migrating your data-driven tests, but before we get into the details, let's briefly recap on what MSTest provides for data-driving tests; the DataSource attribute.

The DataSource attribute specifies a data source from which data points are loaded. The test can then reference the specific data row in the data source from the TestContext's DataRow property. You may recall that we touched on the jack-of-all-trades, master-of-none TestContext back in the entry on outputting from our tests. As MSDN explains, given a table of data rows like this:

FirstNumber	SecondNumber	Sum
0	1	1
1	1	2
2	-3	-1

DataSource is used like this:

[DataSource(@"Provider=Microsoft.SqlServerCe.Client.4.0; Data Source=C:\Data\MathsData.sdf;", "Numbers")]  
[TestMethod()]  
public void AddIntegers_FromDataSourceTest()  
{  
    var target = new Maths();  
  
    // Access the data  
    int x = Convert.ToInt32(TestContext.DataRow["FirstNumber"]);  
    int y = Convert.ToInt32(TestContext.DataRow["SecondNumber"]);   
    int expected = Convert.ToInt32(TestContext.DataRow["Sum"]);  
    int actual = target.IntegerMethod(x, y);  
    Assert.AreEqual(expected, actual,  
        "x:<{0}> y:<{1}>",  
        new object[] {x, y});  
}

I do not recall using this attribute in earnest, and though perhaps others think of it more fondly, I found it a frustration to use. Thankfully, XUnit is much more inline with my intuition¹.

Data-driven test methods in XUnit are called theories and are adorned with the Theory attribute². The Theory attribute is always accompanied by at least one data attribute which tells the test runner where to find data for the theory. There are three built-in attributes for providing data: InlineData, MemberData, and ClassData. Third-party options are also available (check out AutoFixture and its AutoData attribute) and you can create your own if you find it necessary.

InlineData provides a simple way to describe a single test point for your theory; MemberData takes the name of a static member (method, field, or property) and any arguments it might need to generate your data; and ClassData takes a type that can be instantiated to provide the data. A single test point is provided as an array of type object, and while XUnit provides the TheoryData types to allow strongly-typed declaration of test data points, fundamentally, every data source is IEnumerable. Finally, rather than the obscure TestContext.DataRow property, data points are provided to a theory test method via the test method's arguments.

So, given all this information, the above example from MSDN could be expressed as follows:

[InlineData(0, 1, 1)]
[InlineData(1, 1, 2)]
[InlineData(2, -3, -1)]
[Theory]
public void AddIntegers_FromDataTest(int x, int y, int expected)
{
    //Arrange
    var target = new Maths();  
  
    // Act
    int actual = target.IntegerMethod(x, y);  

    // Assert
    Assert.AreEqual(expected, actual,  
        "x:<{0}> y:<{1}>",  
        new object[] {x, y});
}

I took the liberty of using the arrange/act/assert test layout as part of this rewrite as I think it enhances test readability. However, you can see from this example how much easier data-driven testing is under XUnit when compared with traditional MSTest³.

Of course, I totally skipped the fact that the MSTest example used a database for the test data source. That was deliberate to simplify the example, but if we still wanted to use a database to obtain our data points (or some other data source), we can leverage the MemberData or ClassData attributes, or even roll our own.

That brings us to the end of this post on migrating data-driven tests from MSTest to XUnit. This also brings us almost to the end of the whole series on migrating from MSTest to XUnit; if you think I missed something important, please leave a comment. Next time, we will finish up with a look at some of the bits around running XUnit tests such as parallel execution, test runners, and the like.

in case you hadn't noticed, I like XUnit [↩]
instead of [Fact] as on non-data-driven tests [↩]
This approach makes so much sense that MSTest introduced it for phone and WinRT app tests and is bringing it to everyone with MSTest version 2 [↩]

TestContext Equivalence in XUnit2, or How Do I Write Output in XUnit2?

So far, in discussing the migration of MSTest to XUnit2, I have only touched on the basics. First, I covered using the XUnitConverter to make the transition a little easier, then I provided an overview of how the basic MSTest concepts tests, test initialization, and test cleanup were supported. In this post I want to look at the confusing dumping group that is TestContext. My goal with these posts is to provide useful search results for those looking for information on XUnit, especially when migrating from MSTest. For a moment though, let me rant about TestContext.

I am sure that there are people out there who totally get all the values and functions TestContext provides; however, other than writing log messages, I have found the TestContext properties wildly confusing and unhelpful. I somehow doubt I am alone. Not only that, but the inconsistent ways a method gets access to the TestContext dependent on whether it is an instance method or a static method makes things confusing¹.

TestContext Properties

Looking at the documentation from MSDN (shown above), it should be clear to anyone that TestContext is trying to do a lot of different things. There are methods in there for outputting things to the test trace messages, adding results files, and running timers, and properties for getting all sorts of information from directories for results, to the name of the test, to things related to data driven tests. Overall, it is convoluted and confused; do you know the difference between ResultsDirectory, TestResultsDirectory, and TestRunResultsDirectory? Even after working with MSTest for nearly 10 years, I could not begin to tell you. In my opinion, TestContext does too much and is almost always unintuitive to use, so how does XUnit tackle these things?

Well, first of all, XUnit does not even begin to replace the timer stuff because, well, there are plenty of timer options available in the .NET framework, so just use one of them.

Second, XUnit manipulates the current directory when running tests, so the location retrieved from Environment.CurrentDirectory will be where the tests are running and where test data will live. We will focus on data-driven testing in another post, but suffice to say that you do not need to decipher pages of documentation or debug tests to understand where to find your test data or where to output your test results (if you have something to output, of course).

Finally, if you want to write to the test output, XUnit provides an interface that you can inject into your constructor for doing just that and only that; ITestOutputHelper.

ITestOutputHelper

Since the XUnit documentation is very helpful on how to use this interface, I won't go into great detail here. However, for those looking to replace TestContext.WriteLine, this is what you need to do.

using Xunit;
using Xunit.Abstractions;

public class MyTests
{
    private readonly ITestOutputHelper _output;

    public MyTests(ITestOutputHelper output)
    {
        _output = output;
    }

    [Fact]
    public void Test1()
    {
        var stringValue = "a thing to output";
        _output.WriteLine($"My string value is \"{stringValue}\"");
    }
}

The test runner observes from the signature of the class constructor that it requires the ITestOutputHelper interface and injects it, making it available throughout the test execution, including during the Dispose method, if present.

Next time, we will take a look at how XUnit tackles sharing initialization across multiple tests. In the meantime, if you are finding these posts useful or have any questions, please leave a comment.

a property called TestContext with public getter and setter for instance methods; or passed as a parameter for static methods [↩]

TestMethod, TestInitialize, and TestCleanup in XUnit2

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.

The class no longer has an attribute. XUnit knows the class is a test class because it contains tests³.
The tests are decorated with a [Fact] attribute, which is equivalent to [TestMethod].
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.

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

Migrating from MSTest to XUnit 2

We recently migrated most of our testing from the MSTest framework¹ to XUnit 2 (from here on in, I will be referring to this as just XUnit). This was not a change taken lightly since it touched a lot of files, but we were motivated by a number of XUnit features, including reduced need to attribute test classes, easier data-driven tests, and parallel test execution.

Sadly, if you try this you may discover as we did that the XUnit documentation is equal parts super helpful and woefully lacking, depending on what you are trying to do. After hearing yet another colleague lament how hard it was to find information on some feature or other of XUnit, I thought it might be a good idea to document some of the things I have learned and hopefully, introduce yet another helpful XUnit resource to the Internet².

For those not familiar with XUnit, the basics are pretty easy. In fact the existing XUnit documentation includes a handy table mapping concepts in other test frameworks to their XUnit equivalents. You can check that table out for details, but basically, through the use of attributes, constructors, IDisposable, and other interfaces, XUnit uses what I would describe as a more natural approach than other frameworks to concepts like tests, test initialization and cleanup, and test fixtures. Of course, this means that migrating from one framework to XUnit involves a bunch of file editing, but fear not for there is help.

XUnitConverter

The bulk of the migration was made a lot easier by using the XUnitConverter, a tool available in the dotnet/codeformatter GitHub repository. Although it does not take care of everything (beware if you have multiple test classes per file) and, depending on your preferred code format, can mess your formatting up a bit, but it does make the migration a lot easier.

The XUnitConverter runs against a csproj file. You can use PowerShell to recurse your solution and process all your projects like this:

Get-ChildItem -Recurse *.csproj | %{XUnitConverter $_.FullName}

Once the converter has done its thing, it is easy to identify further changes by using the compiler (things don't like to build if something did not work right). Although most things get converted with ease—[TestMethod] becomes [Fact], [TestInitialize] becomes a constructor, complex tests will need a little more assistance to fully migrate. For example, XUnit uses interfaces and fixture classes to replace the kind of shared initialization and cleanup that MSTest provides via the [ClassInitialize] and [ClassCleanup]. We will start tackling these issues next time.

Version 1 of MSTest, not the new and improved MSTest version 2 [↩]
I would like to document my anecdotal information before I even consider tackling something a little more structured like contributing to the official documentation [↩]