test controller method + DataAnnotations - asp.net mvc 3

Question

This is a follow up on this:

other SO post

Is this a good way to test whether the validation based on DataAnnotations works in the controller:

[Test]
public void UserController_CannotCreateUserWithNoLastName()
{
    // Arrange
    var user = new CreateUserViewModel();
    UsersController controller = new UsersController();
    var validationContext = new ValidationContext(user, null, null);
    var validationResults = new System.Collections.Generic.List<ValidationResult>();
    Validator.TryValidateObject(user, validationContext, validationResults);
    foreach (var validationResult in validationResults)
    {
    controller.ModelState.AddModelError("", validationResult.ErrorMessage);
    }

    // Act
    var result = controller.CreateUser(user);

    // Assert
    Assert.IsFalse(controller.ModelState.IsValid);
}

Any improvement suggestions would be very much welcome. I am also wondering whether one usually writes one test for each validation/business rule. Thanks!

Answer 1

Is the code you listed based off of what's found here?

Personally, I write tests like so on a per annotation basis:

    [Test]
    public void CreateEventViewModel_Description_Property_Contains_StringLength_Attribute()
    {
        // Arrange
        PropertyInfo propertyInfo = typeof(CreateEventViewModel)
                                       .GetProperty("Description");
        // Act
        StringLengthAttribute attribute = propertyInfo
                      .GetCustomAttributes(typeof(StringLengthAttribute), true)
            .Cast<StringLengthAttribute>()
            .FirstOrDefault();

        // Assert
        Assert.NotNull(attribute);
        Assert.AreEqual(255, attribute.MaximumLength);
    }

I based this off of some information that Brad Wilson posted some time back. These tests are stored separate of the controller tests. I'm not sure if there's a more efficient way of doing this today (some folks have created more generic helper methods to do this type of testing; I just prefer having explicit tests for each attribute on my own) but it will verify that your data annotations do exist on your view models as expected.

A combination of this type of test, specifically verifying attributes, along with tests to test model state as listed in your previous question

UsersController.ModelState.AddModelError("username", "Bad username"); 

is what I typically go with.