public void SetValidationMessageElement() { // Arrange var mockViewContext = new Mock<ViewContext>(); var viewDataContainer = new Mock<IViewDataContainer>().Object; var htmlHelper = new HtmlHelper(mockViewContext.Object, viewDataContainer); // Act htmlHelper.SetValidationMessageElement("label"); // Act & assert mockViewContext.VerifySet(vc => vc.ValidationMessageElement = "label"); }