TDD - testing business rules/validation in ASP.NET MVC

Question

I am using the sharp architecture so I can easily use mocks etc. in my unit tests and/or during TDD. I have quite complicated business rules and would like to test them at the controller level. I am just wondering how other people do this?

For me validation tests business rules at three levels:

(1) Property level (e.g. property is required) (2) Intra property level (e.g. start date < end date) (3) Persistence level (e.g. name is unique, parent cannot be child of child)

My validation framework also assigns errors to properties. I am just wondering what other people do? Do you write a test for each business rule and check whether the correct error message is assigned to the correct property (i.e. looking at the ASP.MVC ModelState)?

I hope my question makes sense. Thanks a lot!

Best wishes,

Christian

Answer 1

I usually split this in two:

1. Test if the controller behaves correctly when the model is valid and when it's not.
2. Test if the model in combination with a rule engine produces the correct error messages.

The rationale is that when the controller behaves correctly for errors or not, and the model itself validates correctly, then the application will behave correctly. The test setup will also be simpler.

In the simplest case for a post we would probably want the controller to redirect to a result page when everything is fine, but redisplay the same view when there are validation errors:

  [TestClass]
    public class Maintaining_todo_list
    {
        private TodoController controller;

        [TestInitialize]
        public void Setup()
        {
            controller = new TodoController {ControllerContext = new ControllerContext()};
        }

        [TestMethod]
        public void Valid_update_should_redirect_to_list()
        {
            var result = controller.Edit(1, new TodoItem {Text = "todo"});
            result.ShouldRedirectTo("list");
        }

        [TestMethod]
        public void Invalid_update_should_display_same_view()
        {
            var result = controller.Edit(1, new TodoItem {Text = ""});
            result.ShouldDisplayDefaultView();
        }
    }

The model can fail in various ways with different messages:

   [TestClass]
    public class Validating_todo_item
    {
        [TestMethod]
        public void Text_cannot_be_empty()
        {
            var todo = new TodoItem {Text = ""};
            todo.ShouldContainValidationMessage("Text cannot be empty");
        }

        [TestMethod]
        public void Text_cannot_contain_more_than_50_characters()
        {
            var todo = new TodoItem { Text = new string('a', 51) };
            todo.ShouldContainValidationMessage("Text cannot contain more than 50 characters");
        }

        [TestMethod]
        public void Valid_items()
        {
            new TodoItem { Text = new string('a', 1) }.ShouldBeValid();
            new TodoItem { Text = new string('a', 50) }.ShouldBeValid();
        }
    }

(For completeness sake, here are the test helpers)

 internal static class AssertionHelpers
    {
        public static void ShouldRedirectTo(this ActionResult result, string action)
        {
            var redirect = result as RedirectToRouteResult;

            Assert.IsNotNull(redirect);
            Assert.AreEqual(action, redirect.RouteValues["action"]);
            Assert.IsNull(redirect.RouteValues["controller"]);
        }

        public static void ShouldDisplayDefaultView(this ActionResult result)
        {
            var view = result as ViewResult;

            Assert.IsNotNull(view);
            Assert.AreEqual("", view.ViewName);
        }

        public static void ShouldContainValidationMessage(this TodoItem todo, string message)
        {
            var context = new ValidationContext(todo, null, null);
            var results = new List<ValidationResult>();

            Validator.TryValidateObject(todo, context, results, true);

            var errors = results.Select(result => result.ErrorMessage);

            foreach (var error in errors)
            {
                Console.Out.WriteLine(error);
            }

            Assert.IsTrue(errors.Contains(message));
        }

        public static void ShouldBeValid(this TodoItem todo)
        {
            var context = new ValidationContext(todo, null, null);
            var results = new List<ValidationResult>();
            var isValid = Validator.TryValidateObject(todo, context, results, true);
            Assert.IsTrue(isValid);
        }
    }