Unit tests on MVC validation

Question

How can I test that my controller action is putting the correct errors in the ModelState when validating an entity, when I\'m using DataAnnotation validation in MVC 2 Previe

Answer 1

I had been having the same problem, and after reading Pauls answer and comment, I looked for a way of manually validating the view model.

I found this tutorial which explains how to manually validate a ViewModel that uses DataAnnotations. They Key code snippet is towards the end of the post.

I amended the code slightly - in the tutorial the 4th parameter of the TryValidateObject is omitted (validateAllProperties). In order to get all the annotations to Validate, this should be set to true.

Additionaly I refactored the code into a generic method, to make testing of ViewModel validation simple:

    public static void ValidateViewModel(this TController controller, TViewModel viewModelToValidate) 
        where TController : ApiController
    {
        var validationContext = new ValidationContext(viewModelToValidate, null, null);
        var validationResults = new List();
        Validator.TryValidateObject(viewModelToValidate, validationContext, validationResults, true);
        foreach (var validationResult in validationResults)
        {
            controller.ModelState.AddModelError(validationResult.MemberNames.FirstOrDefault() ?? string.Empty, validationResult.ErrorMessage);
        }
    }

So far this has worked really well for us.