Upgrade to XCTest. #258
Description
To be tackled after we drop support for 5.1 and 6.1 (#245), at the end of the 2.0 release cycle, unless Xcode 6 forces our hand by dropping support for XCTest (it is only deprecated as of Beta 6). XCTest only supports iOS 6 and later, and 6 only as of Xcode 6.