Is there any reason not to use Action and Func<T> instead? Since Action and Func<T> are natural types for delegates in C#, using other delegates causes some confusion, e.g. here:

        var getActual = () => "/* get actual value */";
        Assert.That(getActual, Is.EqualTo("expectedValue").After(10000, 500));

Since I'm passing a delegate to Assert method, I'd expect a delegate overload to be invoked. Instead, non-delegate TActual overload is used, and assertion fails - because getActual is Func<string>, not ActualValueDelegate<TActual>.

Therefore, my question is. Would it make sense to to replace TestDelegate and ActualValueDelegate with Action and Func<T> in the next major version?