Cocoa Programming for OS X: The Big Nerd Ranch Guide

Refactoring for Testing

When you write an application without testing in mind, you will often write code that is difficult to test. In Chapter 28, you implemented ScheduleFetcher’s method fetchCoursesUsingCompletionHandler(_:). In that implementation, you call NSURLSession.dataTaskWithRequest(_:completionHandler:). and pass in a complex completion handler which transforms the triple of data, response, and error into a FetchCoursesResult.

As the method is currently implemented, the logic of the completion handler is very difficult to test: testing it requires calling fetchCoursesUsingCompletionHandler(_:) which entails calling an asynchronous HTTP method. To avoid making an HTTP request, you will refactor ScheduleFetcher.

In ScheduleFetcher.swift ...