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 ...

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