Unit Testing HtmlHelper that Needs to Access Data Layer

Question

I am trying to create a unit test for an HtmlHelper that accesses my data layer to get a string. I have looked at a lot of posts around this and I am probably missing something. The problem that I am having is how do I mock the access to my data layer? I usually do my dependency ijection through the constructor, but I cannot here because the html helper needs to be static. So I've setup the injection through a property, but how do I access this from my unit test. Sorry if this is obvious, but its messing me up right now.

Here is what I have -

public static class StringResourceHelper
{

    #region Private Members

    private static IStringResourceService _service;

    #endregion

    #region Public Properties

    private static IStringResourceService Service
    {
        get
        {
            if(_service==null)
            {
                _service = (IStringResourceService)Bootstrapper.Container.Resolve(typeof(IStringResourceService));
            }

            return _service;
        }
    }

    #endregion

    #region Public Methods

    public static string StringResource(this HtmlHelper helper, string label)
    {
        int languageCode;

        if(helper.ViewData["LanguageCode"] == null || !Int32.TryParse(helper.ViewData["LanguageCode"].ToString(), out languageCode))
        {
            languageCode = Constants.LanguageCodes.English;
        }

        return Service.GetString(label, languageCode);
    }

    #endregion

}

How do I mock the Service.GetString call?

Answer 1

To start with I would be weary of any static methods that require a member variable. To me that is a sign that you have a object (likely Singletonly scoped). So my first suggestion would be to promote StringResourceHelper to a none-static class and use DI as normal.

If you can't then does your DI framework of choice support static setter injection? Warning bells go off for me if I see something outside the bootstrap playing with the DI framework as it looks to me as if it is you are using the DI framework as a service locator.

If you can't change the class to be none-static and your DI framework does not support static setter injection then I would either:

Set the DI framework up as part of the tests set up to return mocks or add a setter to StringResourceHelper so it can be controlled.

Answer 2

Disclaimer I work at Typemock

If you need to mock/fake static methods and without changing your code you'll need to use Isolator. Faking the method is done using:

Isolate.WhenCalled(() => Service.GetString(string.empty, 0)).WillReturn(/*insert return value here*/);

If you want to check the arguments passed to Service.GetString use the following:

Isolate.Verify.WasCalledWithExactArguments(() => Service.GetString(/* use expected arguments*/);