Concurrency Test

To complete this task, fill out the loadMessage method below this comment.

Background

There is two data sources fetchMessageOne & fetchMessageTwo that load two parts of a messaage. These mimic loading data from the network and call their completion handlers in 0-2 seconds.

Part 1

This function should fetch both parts of the message (concurrently using GCD or OperationQueue) and join them with a space. e.g if fetchMessageOne completes with "Good" and fetchMessageTwo completes with "morning!" then loadMessage should call it's completion once with the String: "Good morning!" If loading either part of the message takes more than 2 seconds then loadMessage should complete with the String "Unable to load message - Time out exceeded"

The function should only complete once and must always return the full message in the correct order.

Part 2

Refactor this function to use idomatic Swift code. Follow the apple Swift naming guidelines. If you choose you can abstract classes, structs, protocols, enums, generics etc.

Part 3

Refactor this function so it is easy to unit test. Write unit tests that verify both the successful loading & timeout behaviour. These tests must be deterministic.

Part 4

• The completion handler should always be called on the main thread.
• If loadMessage is called on the main thread, loadMessage should not block the main thread.