Sunday, April 24, 2016

How to Order xUnit Tests and Collections

xUnit is an extremely extensible unit testing framework!

If you need to control the order of your unit tests, then all you have to do is implement an ITestCaseOrderer. Once implemented, you just add a TestCaseOrdererAttribute to the top of your test class to use it. Below we use a custom OrderAttribute to order the tests.

To control the order of the test collections you can do a very similar trick by implementing an ITestCollectionOrderer. However, an ITestCollection is not neccessarily associated with a specific class, so to to use attributes to order them you need to use a little reflection. Check out the sample below for details.


/// <summary>
/// Used by CustomOrderer
/// </summary>
public class OrderAttribute : Attribute
    public int I { get; }
    public OrderAttribute(int i)
        I = i;
/// <summary>
/// Custom xUnit test collection orderer that uses the OrderAttribute
/// </summary>
public class CustomTestCollectionOrderer : ITestCollectionOrderer
    public const string TypeName = "xUnitCustom.CustomTestCollectionOrderer";
    public const string AssembyName = "xUnitCustom";
    public IEnumerable<ITestCollection> OrderTestCollections(
        IEnumerable<ITestCollection> testCollections)
        return testCollections.OrderBy(GetOrder);
    /// <summary>
    /// Test collections are not bound to a specific class, however they
    /// are named by default with the type name as a suffix. We try to
    /// get the class name from the DisplayName and then use reflection to
    /// find the class and OrderAttribute.
    /// </summary>
    private static int GetOrder(
        ITestCollection testCollection)
        var i = testCollection.DisplayName.LastIndexOf(' ');
        if (i <= -1)
            return 0;
        var className = testCollection.DisplayName.Substring(i + 1);
        var type = Type.GetType(className);
        if (type == null)
            return 0;
        var attr = type.GetCustomAttribute<OrderAttribute>();
        return attr?.I ?? 0;

Sunday, April 10, 2016

RangeSet for .NET

Update 4/13 - Added support for single value ranges.

What data structure do you use when you need to efficiently check if a number is within a large set of ranges?

If you require that the ranges do not overlap, then it is simple to keep a balanced binary tree of the ranges. Finding if a number is within one of those ranges should only take O(log n) to find. Below is an implementation of a RangedSet that uses a standard .NET SortedSet to store the ranges.

IRangeSet Interface

public interface IRangeSet<in T> where T : IComparable
    void AddRange(T min, T max);
    bool Contains(T findValue);

Friday, April 1, 2016

Thursday, March 31, 2016 Extensions Config v3.3.0

I recently made several updates to the xunit.extensions.config library, which allows you to configure theory data from your app.config file. Here are the links to the source and the NuGet package:

New Features

  • Named Parameter Support

You no longer need to configure your data by parameter index. You can now name your data for each parameter, making the configuration much easier to read and understand.

  • AppSettings Support

You can now use the standard AppSettings section of the App.config to configure your data. If no settings are found, then the framework will fallback to trying to use the standard config section.

  • Default Namespace Option

You can now provide a default namespace for your tests. This reduced the amount of redundant text in your config file, and makes test names much more concise and easy to read.

  • Extensible Data Provider

Don't want to use the existing data providers? Would you rather use a database? Now you can! Just add an AppSettings key for "TestData.ServiceFactory" that provides the fully qualified name of a static method that returns an IConfigTestDataService, and the framework will try to use that to load configuration data.

Wednesday, March 30, 2016

Why method that return a Task should end with Async

I have spoken before about using the Fleck WebSocket server library for .NET, but recently I experienced a small problem with it. Pull request #126 changed several public methods to become async and return a Task instead of void.

This did not follow the recommended naming convention of naming all async methods with the Async suffix.

In my case, this caused us to introduce a bug to a project that was using Fleck. We would ignore Task returned from IWebSocketConnection.Send, and under high load the task scheduler would get backed up.

Even though I do not think that they are going to use it, I created a pull request that updated the the public methods to include the Async suffix. Also, in order to maintain backwards compatibility, I also added obsolete methods to the interfaces without the suffix.

What did I do with the tasks? Rather than write in parallel, I used a concurrent queue and had a background task serially write messages to the connection.


Friday, March 18, 2016

How to Release a Semaphore with a Using Block

I love that .NET has so many useful utilities available in the base framework. I often use the SemaphoreSlim, and I love that it supports async await. However, I don't like always having to create a try finally block around every use call to ensure that the release method gets called.

Below is a simple little extension method that will allow you to place the result of the Semaphore wait into a using block, thus ensuring that the dispose will always release the lock.

SemaphoreSlim Extensions

public static class SemaphoreSlimExtensions
    public static async Task<IDisposable> UseWaitAsync(
        this SemaphoreSlim semaphore, 
        CancellationToken cancelToken = default(CancellationToken))
        await semaphore.WaitAsync(cancelToken).ConfigureAwait(false);
        return new ReleaseWrapper(semaphore);
    private class ReleaseWrapper : IDisposable
        private readonly SemaphoreSlim _semaphore;
        private bool _isDisposed;
        public ReleaseWrapper(SemaphoreSlim semaphore)
            _semaphore = semaphore;
        public void Dispose()
            if (_isDisposed)
            _isDisposed = true;

Saturday, February 27, 2016

Podcast - What should all software developers want in their applications?

Each week, my good friend Zach Mayer and I answer geek culture's most superfluous questions on the QQ-Cast. This past week we turned to the subject of software development, and did a retrospective on my series of blog posts, Three Things that all Applications MUST Have.

QQ Cast - Quest 40 - What should all software developers want in their applications?

  • 00:00 - Mic Check and Introductions
  • 03:55 - Why isn't your application logging?
  • 06:15 - Where is your configuration coming from?
  • 11:00 - Can we talk about Unit Tests for 18 minutes?
  • 29:00 - Is continuous integration necessary?
  • 30:30 - Does automated deployment speed up development?
  • 38:00 - When should you use inversion of control?
  • 49:30 - How intrusive is error reporting for end users?
  • 59:00 - Do you remove user impersonation from production builds?
  • 63:30 - Why is continuous deployment so controversial?
  • 72:15 - Wrap up!


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