Apple has released the stable version of Xcode 9 recently with loads of new features. The most of the iOS developers are saying Xcode 9 is the best release so far as it has great new features that iOS Developers always wanted. You can read more about the Xcode 9 features here.
We have just migrated our existing XCUITest suite to Xcode 9 and found that unit tests written in XCTest passed but the XCUITests stopped working with the following error.
Read more about Main Thread Checker and XCUITests with Xcode 9 at http://shashikantjagtap.net/main-thread-checker-xcuitests-xcode-9/