Unit test an Action with Recaptcha

Question

How I can test the following Action of the controller:

 public ActionResult Edit(User usr)
    {
        if (!Microsoft.Web.Helpers.ReCaptcha.Validate(ConfigurationManager.AppSettings["reCaptchaPrivate"].ToString()))
        {
            ModelState.AddModelError("reCaptcha", PPRR.App_LocalResources.Global.ErrorFillReCaptcha);
            return PartialView("Wrong", usr);
        }
        if (ModelState.IsValid)
        {code..... }}

Answer 1

I would start by abstracting the Captcha validation code:

public interface ICaptchaValidator
{
    bool Validate();
}

and then have my controller look like this:

public class FooController: Controller
{
    private readonly ICaptchaValidator _validator;
    public FooController(ICaptchaValidator validator)
    {
        _validator = validator;
    }

    public ActionResult Edit(User usr)
    {
        if (!_validator.Validate())
        {
            ModelState.AddModelError("reCaptcha", PPRR.App_LocalResources.Global.ErrorFillReCaptcha);
            return PartialView("Wrong", usr);
        }

        ...
    }
}

Now you have weaken the coupling between your controller and the way those captchas are validated. That's a good thing as it makes your controller action far easier to unit test. We have successfully made our controller independent of the actual way validation is implemented.

Now just pick a mocking framework such as Rhino Mocks, Moq, NSubstitute and in your unit test inject a stubbed validator into this controller so that you can define behaviors on it.

Personally I would recommend you MvcContrib.TestHelper (which is based on Rhino Mocks) to test your ASP.NET MVC applications. It has many built-in goodies for mocking the HttpContext and make unit testing easy.

Here's an example of how the validation failure case could be tested:

[TestMethod]
public void FooController_Edit_Action_Should_Return_The_Wrong_Partial_If_Captcha_Validation_Fails()
{
    // arrange
    var validatorStub = MockRepository.GenerateStub<ICaptchaValidator>();
    var sut = new HomeController(validatorStub);
    var user = new User();
    validatorStub.Stub(x => x.Validate()).Return(false);

    // act
    var actual = sut.Edit(user);

    // assert
    actual
        .AssertPartialViewRendered()
        .ForView("Wrong")
        .WithViewData<User>()
        .Equals(user);
    Assert.IsFalse(sut.ModelState.IsValid);
}

Answer 2

As an alternative to Darin's answer, I've previously used a custom ActionFilter that processes the captcha and adds the error to the ModelState. It worked really well and meant that the captcha code wasn't part of the action method itself.