No matching device (UUID) in set at /Users/<username>/Library/Developer/XCTestDevices

Question

I've been getting this error in Xcode 10.1 when running unit tests. It happens quite often.

When running unit tests in Xcode, test might pass or fail a few times. Then, after a few runs, this error appears, with Xcode not being able to launch or communicate with the iOS simulator.

Selecting a different simulator from the list is a workaround, but it gets a bit annoying having to do so. Furthermore, after a few unit test runs in the new selected simulator, the error comes back (with a different UUID).

Closing the simulator app and running the tests again does not solve the issue (same error alert appears). Neither does closing and reopening the project.

One thing noticed is, when Xcode gets in this state, closing Xcode (quitting the application) takes longer than usual. Closing Xcode and relaunching it, then running unit tests, also does fix the issue.

Answer 1

• Window -> Devices & Simulators
• Delete simulator
• Add same simulator
• Run tests again