What Should a Custom Assert Class Do if the Assert Fails?

Question

I created a custom Assert class for unit testing, and I'm not sure what to do when I want to notify that the test has failed:

public static class MyAssert
{
    public static void Contains(File file, string text){
        if(!ContainText(file, text)){
            // what to do here?
        }
    }
}

I reflected the Microsoft.VisualStudio.TestTools.UnitTesting.Assert Class and noticed that it calls HandleFail:

internal static void HandleFail(string assertionName, string message, params object[] parameters)
{
  string str = string.Empty;
  if (!string.IsNullOrEmpty(message))
    str = parameters != null ? string.Format((IFormatProvider) CultureInfo.CurrentCulture, Assert.ReplaceNulls((object) message), parameters) : Assert.ReplaceNulls((object) message);
  if (Assert.AssertionFailure != null)
    Assert.AssertionFailure((object) null, EventArgs.Empty);
  throw new AssertFailedException((string) FrameworkMessages.AssertionFailed((object) assertionName, (object) str));
}

But this is an internal method. I could use reflection to call it, or maybe it makes more sense to throw an AssertFailedException? Is there another option that I'm missing?

Answer 1

In order to make a custom Assert method as operate exactly like the standard assert methods, you must throw a new AssertFailedException. At first I really didn't like this because the debugger stops on the AssertFailedException throw statement, and not on the actual assert statement. After a little more research I discovered the DebuggerHidden method attribute and viola, my assert performs as desired.

[DebuggerHidden]
public static void Contains(File file, string text){
    if(!ContainText(file, text)){
        HandleFail("MyAssert.Contains", null, null);
    }
}

[DebuggerHidden]
private static void HandleFail(string assertName, string message, params object[] parameters )
{
    message = message ?? String.Empty;
    if (parameters == null)
    {
        throw new AssertFailedException(String.Format("{0} failed. {1}", assertName, message));
    }
    else
    {
        throw new AssertFailedException(String.Format("{0} failed. {1}", assertName, String.Format(message, parameters)));
    }
}

Answer 2

Just call a standard Assert from inside your custom one.