Repeat mstest test run multiple times

Question

Some of my mstest unit tests help detect multi-threading race conditions, and as such they are most useful when run many times in a row, but I only want to do this for specific test runs -- not all the time.

Is there a way to configure mstest (in the Test List Editor preferably) to run a test multiple times?

Answer 1

I needed to do something similar, so I came up with a solution to this.

It's not simple, but once everything is setup you can reuse it across projects. I also have a download of this code on GitHub (https://github.com/johnkoerner/MSTestLooper), but in case that goes away at some point, here is how I did it.

First we create an attribute that we will apply to our class to tell it run all the tests multiple times. Do all of this in a separate assembly, because the DLL needs to live in a special location.

[Serializable]
public class TestLooperAttribute :  TestClassExtensionAttribute
{
    private static readonly Uri thisGuy = new Uri("urn:TestLooperAttribute");

    private string _PropertyName;
    public string PropertyName
    {
        get
        { return _PropertyName; }
        set
        {
            _PropertyName = value;
        }
    }
    public override Uri ExtensionId
    {

        get {
            return thisGuy; }
    }


        public override TestExtensionExecution GetExecution()
    {

        return new TestLooperExecution(PropertyName);
    }
}

Next we have to create a custom test class execution class:

class TestLooperExecution : TestExtensionExecution
{
    private string PropertyName;

    public TestLooperExecution(string PropertyName)
    {
        this.PropertyName = PropertyName;
    }

    public override ITestMethodInvoker CreateTestMethodInvoker(TestMethodInvokerContext InvokerContext)
    {
        return new TestLooperInvoker(InvokerContext, PropertyName);
    }

    public override void Dispose()
    {
        //TODO: Free, release or reset native resources
    }

    public override void Initialize(TestExecution Execution)
    {
        //TODO: Wire up event handlers for test events if needed

    }
}

Finally we add a custom invoker, which is where we perform the looping:

class TestLooperInvoker : ITestMethodInvoker
{
    private TestMethodInvokerContext m_invokerContext;
    private string PropertyName;

    public TestLooperInvoker(TestMethodInvokerContext InvokerContext, string PropertyName)
    {
        m_invokerContext = InvokerContext;
        this.PropertyName = PropertyName;
    }

    public TestMethodInvokerResult Invoke(params object[] args)
    {

        // Our helper results class to aggregate our test results
        HelperTestResults results = new HelperTestResults();

        IEnumerable<object> objects = m_invokerContext.TestContext.Properties[PropertyName] as IEnumerable<object>;

        foreach (var d in objects)
            results.AddTestResult(m_invokerContext.InnerInvoker.Invoke(d), new object[1] { d.GetType().ToString()});

        var output = results.GetAllResults();
        m_invokerContext.TestContext.WriteLine(output.ExtensionResult.ToString());

        return output;
    }
}

The HelperTestResults class just builds up strings for output, you can handle this how you want and I don't want to include that code because it will just make this post that much longer.

Compile this into a DLL and then you need to copy it to

C:\Program Files (x86)\Microsoft Visual Studio 11.0\Common7\IDE\PublicAssemblies

You also have to create a registry entry for the class:

Windows Registry Editor Version 5.00 
[HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\VisualStudio\11.0\EnterpriseTools\QualityTools\TestTypes\{13cdc9d9-ddb5-4fa4-a97d-d965ccfc6d4b}\TestTypeExtensions\TestLooperAttribute]
"AttributeProvider"="TestLooper.TestLooperAttribute, TestLooper"

Now that you have all of that done, you can finally use the class:

using System;
using Microsoft.VisualStudio.TestTools.UnitTesting;
using TestLooper;
using System.Collections.Generic;
namespace UnitTestSamples
{
    [TestLooper(PropertyName="strings")]
    public class UnitTest1
    {
        public static List<String> strings = new List<String>();
        private TestContext testContextInstance;

        public TestContext TestContext
        {
            get
            {
                return testContextInstance;
            }
            set
            {
                testContextInstance = value;
            }
        }
        [ClassInitialize()]
        public static void Init(TestContext x)
        {
            strings.Add("A");
            strings.Add("B");
            strings.Add("C");
            strings.Add("D");

        }

        [TestInitialize()]
        public void TestInit()
        {
            if (!TestContext.Properties.Contains("strings"))
            testContextInstance.Properties.Add("strings", strings);
        }

        [TestMethod]
        [DataSource("Microsoft.VisualStudio.TestTools.DataSource.CSV", "DataDriven1.csv", "DataDriven1#csv", DataAccessMethod.Sequential)]
        [DeploymentItem("DataDriven1.csv")]
        public void TestMethodStrings(string s)

        {
            int value1 = Convert.ToInt32(TestContext.DataRow["Col1"]); ;
            TestContext.WriteLine(String.Format("{0}:{1}", s, value1));
        }
    }
}

Notice that our test method accepts a parameter, which comes from the test looper. I also show this using a data driven test, to show you can combine the two together to generate large permutations across your data sets.