public void UseCase() { var appender = new ConsoleAppender(); _wrapper = new Mock <IConsoleWrapper>(); _wrapper.Setup(x => x.WriteLine(It.IsAny <string>())).Callback <string>(x => _lastLine = x); appender.SetFirstField(_wrapper.Object); appender.Append(new LogEvent(0, LogLevel.Info, "A topic", "Some Info", DateTime.Now, 0, Thread.CurrentThread.ManagedThreadId.ToString(), 1)); var end = " - [Info] A topic: Some Info [" + Thread.CurrentThread.ManagedThreadId + "]"; Check.That(_lastLine.EndsWith(end)) .IsTrue(_lastLine + " should end with " + end); }