The short answer
Yes. Rebuilt or re-downloaded automatically when needed.
What is it?
When you run tests in parallel, Xcode clones your simulator several times so each clone can run part of the test suite. The clones are stored in ~/Library/Developer/XCTestDevices, each with its own copy of the app under test and its data, and they can add up to several gigabytes.
What happens if you delete it?
Xcode creates fresh clones the next time you run tests in parallel; the first run is slightly slower. Nothing in your projects is affected.
How to remove it properly
Quit Xcode and make sure no tests are running, then move ~/Library/Developer/XCTestDevices to the Trash using Finder’s Go › Go to Folder….
Quit the app that uses it, then move it to the Trash. Empty the Trash when you’re sure.
How MoreRoom helps
MoreRoom recognises this item, shows its real size and when it was last used, and labels it “Safe to remove”. In the free version you can move it to the Trash in one click, with Undo; Pro collects every safe item at once.
Frequently asked questions
Is it safe to delete the XCTestDevices folder on Mac?
Yes. Rebuilt or re-downloaded automatically when needed. Xcode creates fresh clones the next time you run tests in parallel; the first run is slightly slower. Nothing in your projects is affected.
Will Test simulator clones come back after I delete it?
Yes. Xcode creates fresh clones the next time you run tests in parallel; the first run is slightly slower. Nothing in your projects is affected.
How do I remove Test simulator clones properly?
Quit Xcode and make sure no tests are running, then move ~/Library/Developer/XCTestDevices to the Trash using Finder’s Go › Go to Folder….