Tag: .NET

New Job, New Tech

Hello, world!

You might have noticed I took a little break from my blog recently. It was not intentional; things just got away from me a bit the last few months as I found a new job and had a nice vacation to see family in England (as well as a side trip to Edinburgh and the famous Fringe festival). Perhaps I will post more on the vacation another time; right now, I want to share my job news.

After a fantastic four years with CareEvolution, Inc., I recently accepted a software engineering position with Khan Academy. I am only a few weeks into my new position and I am still incredibly excited to have this opportunity. Not only am I working with some incredible people, we have tasked ourselves with an outstanding mission.

Our mission is to provide a free, world‑class education for anyone, anywhere.1

Leaving CareEvolution, Inc. was a difficult decision. Not only did it mean leaving behind extraordinary colleagues, it also meant leaving behind PowerShell, C#, Angular, and .NET as a part of my day-to-day profession. Instead, I will be working with React, Redux, Apollo, and Python. There is much for me to learn and, I hope, for me to blog about as I learn it. That said, I still love .NET things and will continue to tinker with them in my personal time2.

Of course, like my passion for .NET, some things will remain the same. Most significantly for me, the position is still remote and as such, provides me with great opportunities for personal growth as an offsite colleague and employee. I openly3 struggled with that while at CareEvolution, Inc. I hope that at Khan Academy, I can learn which parts of that struggle were down to the need for personal growth, and which, if any, were organisational. If I can, I will coalesce lessons I learn into a meaningful collection of tips that others might use to adapt their personal and organisational culture around remote work and off-site workers.

Finally, this blog is still my blog, these are my personal musings; nothing I post here represents the views of my employer. Thank you for your readership and your patience during my blog hiatus. As they say at work, onward!

Featured Image by Todd Quackenbush on Unsplash

  1. https://www.khanacademy.org/about [↩]
  2. I have already started developing .NET core on OSX [↩]
  3. perhaps too openly [↩]

C#7: Throw Expressions and More Expression-bodied Members

In this installment of my look at C#7, we will take a look at some nice syntactical enhancements, including the first ever community contribution to the C# language implementation. Before we get started, here is a summary of what I am covering in this series on C#7.

Throw Expressions

We have all written code like this1:

public class MyApiType
{
    private object _loadedResource;
    private object _someProperty;

    public MyApiType()
    {
        _loadedResource = LoadResource();
        if (_loadedResource == null) throw new InvalidOperationException();
    }

    public object SomeProperty
    {
        get
        {
            return _someProperty;
        }
    
        set
        {
            if (value == null) throw new ArgumentNullException();
            _someProperty = value;
        }
    }
}

I have omitted the exception arguments for brevity, but you should hopefully recognise the sort of sanity checking to which I am referring within the highlighted lines.

With throw expressions, we can now combine assignment, the null-coalescing operator2, and throw to create succinct validation code. This means that the example above can be simplified to not even need the constructor.

public class MyApiType
{
    private object _loadedResource = LoadResource() ?? throw new InvalidOperationException();
    private object _someProperty;

    public object SomeProperty
    {
        get
        {
            return _someProperty;
        }
    
        set
        {
            _someProperty = value ?? throw new ArgumentNullException();
        }
    }
}

The highlighted lines are equivalent to the code we had earlier, but now we are able to use throw as part of the expression. The introduction of throw expressions means that we can now throw exceptions in conditional and null-coalescing expressions, as well as some lambda methods where it was previously not possible to do so. Not only that, but when combined with expression-bodied members, we can write some very expressive yet terse code.

Expression-bodied Members

With C#6 we got expression-bodied members, which allowed us to express simple methods using lambda-like syntax. However, this new syntax was limited to methods and read-only properties. Via the first ever community contribution to C#3, C#7 expands this syntax to cover constructors, finalizers, and property accessors.

If we take the property example we had before, containing our throw expression as part of  property set accessor, we can now write it as:

public object SomeProperty
{
    get => _someProperty;
    set => _someProperty = value ?? throw new ArgumentNullException();
}

I won't bother with examples for constructors or finalizers; the main documentation is pretty clear on those and I am not convinced the syntax will be used very often in those cases. Constructors are rarely so simple that the expression-bodied syntax makes sense, and finalizers are so rarely needed4 that most of us will not get an opportunity to write one at all, expression-bodied or otherwise.

In Conclusion

These simple additions to the C# syntax enable us to write terse code without losing clarity, which is always a good thing. Not only that, but we have reached a landmark event; community contributions to C#. This contribution may be a little tame when compared with some of the other features coming in C#7, but it bodes well for the future of the language in its new, open source home.

Next time, we will take a look at the highly anticipated pattern matching. Until then, feel free to leave a comment, or read more about C#7 on my blog and on the official documentation.

  1. Let's ignore the nastiness of throwing exceptions during construction [↩]
  2. You remember Elvis, right?? [↩]
  3. Source: https://docs.microsoft.com/en-us/dotnet/articles/csharp/csharp-7#more-expression-bodied-members [↩]
  4. If you find yourself writing a finalizer, I recommend you make sure you really need it; there is probably a better way [↩]

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.

  1. in case you hadn't noticed, I like XUnit [↩]
  2. instead of [Fact] as on non-data-driven tests [↩]
  3. 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 [↩]

AssemblyInitialize, AssemblyCleanup and Sharing State Between Test Classes in XUnit

We have covered quite a bit in this series on migrating from MSTest to XUnit and we have not even got to the coolest bit yet; data-driven theories. If that is what you are waiting for, you will have to wait a little longer. Before we get there, I want to cover one last piece of test initialization as provided in MSTest by the AssemblyInitialize and AssemblyCleanup attributes.

As we saw in previous posts, we can use the test class constructor and Dispose() for TestInitialize and TestCleanup, and IClassFixture and fixture classes for ClassInitialize and ClassCleanup.  For the assembly equivalents, we use collections and the ICollectionFixture interface.

A collection is defined by a set of test classes and a collection definition. A test class is designated as being part of a specific collection by decorating the class with the Collection attribute, which provides the collection name. A corresponding class decorated with the CollectionDefinition attribute should also exist as this is where any collection fixtures are defined. All classes that share the same collection name will share the collection fixtures from which the definition class derives.

public class MyFirstFixture
{
    public MyFirstFixture()
    {
        // Some initialization
    }
}

public class MySecondFixture : IDisposable
{
    public MySecondFixture()
    {
        // Some initialization
    }

    public void Dispose()
    {
        // Some cleanup
    }
}

[CollectionDefinition("MyCollection")]
public class MyCollectionDefinition : ICollectionFixture<MyFirstFixture>, ICollectionFixture<MySecondFixture>
{
    //Nothing needed here
}

[Collection("MyCollection")]
public class TestClass1
{
    [Fact]
    public void TestMethod1()
    {
        // Do some testing
    }
}

[Collection("MyCollection")]
public class TestClass2
{
    [Fact]
    public void TestMethod1()
    {
        // Do some more testing
    }
}

The example code above shows a collection definition with two fixtures and two test classes defined as part of that collection. Note how the fixtures control initialization and cleanup using constructors and IDisposable 1 . We can modify those classes to reference the collection fixtures just as we did with class-level fixtures; by referencing the fixture in the constructor arguments as shown here.

[Collection("MyCollection")]
public class TestClass1
{
    public TestClass1(MySecondFixture fixture)
    {
        // Do something with the collection fixture
    }

    [Fact]
    public void TestMethod1()
    {
        // Do some testing
    }
}

I really like this approach over the attributed static methods of MSTest. This seems to more easily support code reuse and makes intentions much clearer, separating the concerns of tests (defined in the test class) from fixtures (defined by the fixture types). The downside is that fixture types do not get access to the ITestOutputHelper interface so if you want your fixtures to output diagnostic information, you should consider a logging library like Common.Logging. Also, your fixture types must be in the same assembly as your tests. Of course, that doesn't preclude the fixtures from using types outside of the assembly, so you can always put shared implementation between test assemblies in some other class library.

And that brings our migration of shared initialization to a close. You can find more information on sharing context across tests on the xunit site. Next up, we will look at data-driven tests. Thank you for your time. If you have any questions, please leave a comment.

  1. A fixture type can used with IClassFixture<T> or ICollectionFixture<T> [↩]

ClassInitialize, ClassCleanup, and Sharing Data Across Tests in XUnit2

So far in this series on migrating from MSTest to XUnit, we have looked at:

In this post, we will look at how we can share setup and cleanup code across tests in a test class in XUnit. MSTest allows you to define shared setup and cleanup code for an entire test class by using methods decorated with the ClassInitialize and ClassCleanup attributes. Unlike their counterparts, TestInitialize and TestCleanup, methods decorated with these class-level attributes are executed just once per class, rather than once per test in the class. Using these class-level attributes, we can execute code, generate fixture objects, and load test data that can be used across all tests in the class without having the overhead of repeating this for every test in the class. This is useful when that initialization or cleanup is expensive, such as creating a database connection, or loading several data files.

As we have seen so far, XUnit is light on decorating non-test methods with attributes, instead relying on language syntax that mirrors the purpose of the code. In the case of TestInitialize and TestCleanup, XUnit uses the test class constructor and IDisposable. It should come as no surprise that this pattern is also used when it comes to class-level initialization and cleanup.

IClassFixture<T>

There are two parts to shared initialization and cleanup in XUnit: declaring what shared items a test class uses, and referencing them within test methods.

To declare specific setup is required, a test class must be derived from IClassFixture for each shared setup/cleanup. The T in IClassFixture is the actual type responsible for the initialization and cleanup via its constructor and IDisposable implementation.

public class MyFixture : IDisposable
{
    public MyFixture()
    {
        // Setup here
    }

    public void Dispose()
    {
        // Cleanup here
    }
}
public class MyTests : IClassFixture<MyFixture>
{
    [Fact]
    public void Test()
    {
        // Do something knowing that MyFixture was instantiated
    }
}

The XUnit test runner sees that your test class is deriving from IClassFixture and ensures that an instance of MyFixture is created before your tests are run and disposed of when all the tests are completed. I really like this approach over the MSTest equivalent, as it moves the setup and initialization from being about the test class to being about the test fixture, the thing being setup. You can even have more than one fixture, so if you use two databases in your tests, you can have one fixture for each database and explicitly specify the use of each. It also means that you can set things that are supposed to be immutable for the duration of tests to be readonly and enforce that immutability. This is even clearer when referencing fixtures in tests.

public class MyTests : IClassFixture<MyFixture>
{
    private readonly MyFixture _fixture;

    public MyTests(MyFixture fixture)
    {
        _fixture = fixture;
    }

    [Fact]
    public void Test()
    {
        // Do something with _fixture
    }
}

As shown in the preceding example, to reference a test fixture in your test class methods, you just need to add a corresponding argument to the constructor and XUnit will inject the fixture. You can then use the fixture, and assign it or something obtained from it to a member variable of your class. Not only that, but you can mark that member as readonly and be explicit about what tests can and cannot do to your test state. Personally, this approach to shared initialization and cleanup feels much more intuitive. I can easily reuse my initialization and setup code without cluttering my test classes unnecessarily, and I can be explicit about the immutability of any shared state or setup.

And that is it; now you not only know how to share repeatable setup across tests (as provided by TestInitialize and TestCleanup in MSTest), but also how to do the same for setup across the whole test class (as MSTest does with ClassIntialize and ClassSetup).

But, what of AssemblyInitialize and AssemblyCleanup? Well, that's probably a good place to start in the next post. As always, you are welcome to leave a comment letting me know how you are liking this series on migrating to XUnit, or perhaps bringing up something that you'd like me to cover.