How to unit test the DataAnnotationsModelBinder in ASP.NET MVC 2

I'm using ASP.NET MVC 2 with DataAnnotation attributes sprinkled on properties like so:

public class LogOnViewModel
{
    [Required]
    public string UserName { get; set; }

    [Required]
    public string Password { get; set; }

    [Required]
    public string Domain { get; set; }
}

I have a unit test which checks that the current view is rendered when validation fails. However, I'm manually adding errors to the ModelState to get it to work:

    [Test]
    public void TestThatLogOnActionRedirectsToLogOnViewIfValidationFails()
    {
        //create a invalid view model
        var model = new LogOnViewModel {UserName = "jsmith"};

        //Can I avoid doing this manually?
        //populate Model State Errors Collection
        _accountController.ModelState.AddModelError("FirstName", "First Name Required");
        _accountController.ModelState.AddModelError("LastName", "Last Name Required");

        var result = _accountController.LogOn(model);

        result.AssertViewRendered()
            .ForView(Constants.Views.LogOn)
            .WithViewData<LogOnViewModel>();
    }

Is there a way to interact with the ModelBinder either directly or indirectly in a unit test? For e开发者_StackOverflowxample:

    [Test]
    public void TestThatLogOnActionRedirectsToLogOnViewIfValidationFails()
    {
        //create a invalid view model
        var model = new LogOnViewModel {UserName = "jsmith"};

        //validate model
        //not sure about the api call...
        var validationResults = new DataAnnotationsModelBinder().Validate(model);

        _accountController.ModelState.Merge(validationResults);
        var result = _accountController.LogOn(model);

        result.AssertViewRendered()
            .ForView(Constants.Views.LogOn)
            .WithViewData<LogOnViewModel>();
    }

Brad Wilson has a nice blogpost about the DataAnnotationsModelBinder, including how to unit test it: http://bradwilson.typepad.com/blog/2009/04/dataannotations-and-aspnet-mvc.html

I usually unit test my model validation setup by directly calling the facade methods of System.ComponentModel.DataAnnotations.Validator.

I wrote a article on the subject http://timoch.com/blog/2013/06/unit-testing-model-validation-with-mvcs-dataannotations/

I end up with code like this (the article show a cleaner and reusable unit test base class for model validation)

[Test]
[TestCaseSource("ValidationRule_Source")]
public void ValidationRule(ValidateRuleSpec spec) {
    // Arrange
    var model = CreateValidPersonModel();
    // Apply bad valud
    model.GetType().GetProperty(spec.MemberName).SetValue(model, spec.BadValue);

    // Act
    var validationResults = new List<ValidationResult>();
    var success = Validator.TryValidateObject(model, new ValidationContext(model), validationResults, true);

    // Assert
    Expect(success, False);
    Expect(validationResults.Count, EqualTo(1));
    Expect(validationResults.SingleOrDefault(r => r.MemberNames.Contains(spec.MemberName)), Not.Null);
}

public IEnumerable<ValidateRuleSpec> ValidationRule_Source() {
    yield return new ValidateRuleSpec() {
        BadValue = null,
        MemberName = "FirstName"
    };
    yield return new ValidateRuleSpec() {
        BadValue = string.Empty,
        MemberName = "FirstName"
    };
    yield return new ValidateRuleSpec() {
        BadValue = null,
        MemberName = "LastName"
    };
    /* ... */
}

I don't like trusting code to just work so I systematically write unit test for my model validation code. However, I do trust the framework/model binder to execute validation. This unit test allows me to write controller that trust the validation is OK.