Ignore Trace message when running Test

Question

For a tracing purpose, I have to log every use of a method made by a user. I'm using System.Diagnostics.Trace to fill this purpose, but I'm encountering a problem when running test over these method.

Trace.TraceInformation($"L'utilisateur {HttpContext.Current.User.Identity.Name} a fait une recherche à partir de l'identifiant {ID} ");

This little code is working well on my application, but when it comes to testing, it's not working anymore (due to HttpContext.Current.User being undefined).

How can I potentially mock this or just tell my xUnit to ignore the trace while testing?

Answer 1

I would recommend that you hide your tracing logic behind an interface which can be mocked out.

For example, you could declare an interface as below:

public interface ITraceWriter
{
    void TraceInfo(string traceText);
}

The next step would be to implement this interface as a tracing behaviour:

public class UserTraceWriter : ITraceWriter
{
    public void TraceInfo(string traceText)
    {
        Trace.TraceInformation($"User {HttpContext.Current.User.Identity.Name} {traceText}");
    }
}

You would need to inject the ITraceWriter into your class responsible for performing user actions, for example:

public class UserDoSomethingClass
{
    private readonly ITraceWriter writer;

    public UserDoSomethingClass(ITraceWriter writer)
    {
        this.writer = writer;
    }

    public void DoSomething()
    {
        // the user did something.

        this.writer.TraceInfo("did something");
    }
}

Finally, this would enable you to safely test the class:

 var mockTraceWriter = new Mock<ITraceWriter>();

 mockTraceWriter.Setup(w => w.TraceInfo(It.IsAny<string>()));

 var testClass = new UserDoSomethingClass(mockTraceWriter.Object);

 testClass.DoSomething();