public void TryValidate_ShouldShowMessageBoxAndReturnsFalse_WhenValueIsNotAnInt(string value) { mSut.Value = value; IMessageBoxService messageBoxService = Substitute.For <IMessageBoxService>(); Assert.IsFalse(mSut.TryValidate(messageBoxService)); messageBoxService.Received(1).ShowError("Buffer size must be a valid integer."); }