public void ErrorMessage() { #pragma warning disable CA1303 //warning CA1303: Method 'void ExceptionExtemsionsTest.ErrorMessage()' passes a literal string as parameter 'message' of a call to var x = new FileNotFoundException("bla-blah"); Console.WriteLine($"? {x.Format()}"); Assert.That(x.Format(), Is.EqualTo($"FileNotFoundException: bla-blah{Environment.NewLine}")); var y = new IOException("with inner!", new FileNotFoundException("none", new Exception("more"))); Console.WriteLine($"? {y.Format(4)}"); Assert.That(y.Format(2), Is.EqualTo($"IOException: with inner!{Environment.NewLine} FileNotFoundException: none{Environment.NewLine} Exception: more{Environment.NewLine}")); #pragma warning restore CA1303 }