public void ShouldUpdateBindableValidationHelperIsValidProperty() { const string nameErrorMessage = "Name should not be empty."; var view = new TestView(new TestViewModel { Name = string.Empty }); view.ViewModel.NameRule = view .ViewModel .ValidationRule( viewModelProperty => viewModelProperty.Name, s => !string.IsNullOrEmpty(s), nameErrorMessage); view.OneWayBind(view.ViewModel, vm => vm.NameRule.IsValid, v => v.IsNameValid); view.OneWayBind(view.ViewModel, vm => vm.NameRule.Message, v => v.NameErrorLabel, s => s.ToSingleLine()); Assert.False(view.IsNameValid); Assert.Equal(nameErrorMessage, view.NameErrorLabel); view.ViewModel.Name = "Bingo"; Assert.True(view.IsNameValid); Assert.Empty(view.NameErrorLabel); }