Unit-testing an RSS feed parser
By breaking the code into separate methods, you've made it easier to read, which is good. You've not made it easier to test though (unless you expose those methods to the test framework, which then creates a leaky abstraction and brittle tests). Therefore all you should be testing with your revised code is ParseResponse itself. ParseResponse has lots of side-effects though, so is hard to test.

The solution is to decouple those side-effect causing parts of the code and to inject them:

public FeedSummary ParseResponse(string rssFeed,
                                 IXMLLoader loader,
                                 IXMLSanitizer sanitizer,
                                 IFeedCreator feedCreator)
{
    var doc = loader.LoadXml(rssFeed);
    var cleanData = sanitizer.SanitizeXml(doc);
    var feed = feedCreator.CreateFeed(cleanData);
    return ParseFeed(feed);
}


The you can create implementations of IXMLLoader etc that can be individually tested with integration tests and provide mocks for testing ParseResponse itself.