Unit Testing TelemetryProcessor and TelemetryInitializer (Application Insights)?

Question

I've been looking around the web for a way to unit test my processor and initializer. So far, I have the following code setup from another article, yet I'm a bit lost in how to proceed.

public class TelemetryClientTests
{
    private TelemetryClient telemetryClient;
    private List<ITelemetry> sendItems;

    [TestInitialize]
    public void TestInit()
    {
        var httpContext = Substitute.For<IHttpContextAccessor>();
        var configuration = new TelemetryConfiguration();
        //this.sendItems = new List<ITelemetry>();
        configuration.TelemetryChannel = new RequeteTelemtry();
        configuration.InstrumentationKey = Guid.NewGuid().ToString();
        configuration.TelemetryInitializers.Add(new OperationCorrelationTelemetryInitializer());
        this.telemetryClient = new TelemetryClient(configuration);
    }

    /// <summary>
    /// Ensure that context being propagated via async/await.
    /// </summary>
    [TestMethod]
    public void ContextPropogatesThruAsyncAwait()
    {
        var task = this.TestAsync();
        task.Wait();
    }
}

I'm not sure where I should add my telemtryprocessor so that Application Inisight knows that I'm unit testing it. If anybody knows how to do it, it would be greatly appreciated.

Answer 1

This is an example from one of services where we have unit tests for our telemetry initializers.

First, we have NullTelemetryProcessor. It has two roles: it prevents data to be actually sent to Application Insights services; it stores all items in memory instead (so it is possible to use them for asserts).

Note, telemetry processors are run after telemetry initializers.

public class NullTelemetryProcessor : ITelemetryProcessor
{
    public List<ITelemetry> Items = new List<ITelemetry>();

    public void Process(ITelemetry item)
    {
        this.Items.Add(item);
    }
}

Then we register it:

[TestInitialize]
public void Initialize()
{
    // Initialization of a telemetry configuration
    this.telemetryConfiguration = new TelemetryConfiguration();

    // Adding a telemetry processor which prevents actually sending anything
    this.nullTelemetryProcessor = new NullTelemetryProcessor();
    TelemetryProcessorChainBuilder builder = this.telemetryConfiguration.TelemetryProcessorChainBuilder;
    builder.Use(next => this.nullTelemetryProcessor);
    builder.Build();
}

Then a test might look like this:

[TestMethod]
public void AppInsightsTelemetryClient_TrackException()
{
    // Act
    this.telemetryClient.TrackException(new Exception("myexception"));
    this.telemetryClient.Flush();

    // Assert
    Assert.AreEqual(1, this.nullTelemetryProcessor.Items.Count);
    ExceptionTelemetry telemetryItem = this.nullTelemetryProcessor.Items[0] as ExceptionTelemetry;
    Assert.IsNotNull(telemetryItem);
    Assert.IsNull(telemetryItem.Context?.Operation?.ParentId);
    Assert.IsNull(telemetryItem.Context?.Operation?.Id);
}