Question

As the title, the code itself as following

internal static class ThumbnailPresentationLogic
    {
        public static string GetThumbnailUrl(List<Image> images)
        {
            if (images == null || images.FirstOrDefault() == null)
            {
                return ImageRetrievalConfiguration.MiniDefaultImageFullUrl;
            }

            Image latestImage = (from image in images
                                 orderby image.CreatedDate descending
                                 select image).First();

            Uri fullUrl;

            return 
                Uri.TryCreate(new Uri(ImageRetrievalConfiguration.GetConfig().ImageRepositoryName), latestImage.FileName,
                    out fullUrl)
                    ? fullUrl.AbsoluteUri
                    : ImageRetrievalConfiguration.MiniDefaultImageFullUrl;
        }
    }

I don’t want the unit test go through any methods in ImageRetrievalConfiguration class, so how can I mock ImageRetrievalConfiguration and pass it into ThumbnailPresentationLogic class ??

Answer 1

How about you split the method into two – one of which takes a “base URI” and “default Url” and one of which doesn’t:

internal static class ThumbnailPresentationLogic
{
    public static string GetThumbnailUrl(List<Image> images)
    {
        return GetThumbnailUrl(images,
           new Uri(ImageRetrievalConfiguration.GetConfig().ImageRepositoryName),
           ImageRetrievalConfiguration.MiniDefaultImageFullUrl);
    }

    public static string GetThumbnailUrl(List<Image> images, Uri baseUri,
        string defaultImageFullUrl)
    {
        if (images == null || images.FirstOrDefault() == null)
        {
            return defaultImageFullUrl;
        }

        Image latestImage = (from image in images
                             orderby image.CreatedDate descending
                             select image).First();

        Uri fullUrl;

        return 
            Uri.TryCreate(baseUri, latestImage.FileName, out fullUrl)
                ? fullUrl.AbsoluteUri
                : defaultImageFullUrl;
    }
}

Then you can test the logic in the “three-parameter” overload, but the public method doesn’t really contain any logic. You won’t get 100% coverage, but you’ll be able to test the real logic involved.