xcodebuild test : Could not launch simulator: -10827

Go to the apple icon (top left of screen), then force quit then select the simulator

Run the project again

I had exact same issue. It happens because Mac OS X doesn't allow an iOS simulator to run in the BACKGROUND.

If you are constructing a Jenkins CI environment, and trying to unit test via the simulator, you can't run the simulator, because Jenkins is basically run as a DAEMON. This also happens if you're running the tests behind environments like tmux or screen.

Here is a great tutorial to read that can help you fix this.

Cheers!

For me this helped - close XCode & Simulator (if running) - open Terminal and type:

ps -ax | grep simdeviceio | grep -v grep

this had some output on my Mac:

50755   ??  Ss     0:00.67 /Library/Developer/PrivateFrameworks/CoreSimulator.framework/Versions/A/Resources/SimStreamProcessorServices.simdeviceio/Contents/XPCServices/SimStreamProcessorService.xpc/Contents/MacOS/SimStreamProcessorService
50756   ??  Ss     0:00.07 /Library/Developer/PrivateFrameworks/CoreSimulator.framework/Versions/A/Resources/SimAudioProcessorServices.simdeviceio/Contents/XPCServices/SimAudioProcessorService.xpc/Contents/MacOS/SimAudioProcessorService

This 2 processes could either manually be killed by typing their PIDs (first number in above lines) with a kill command:

kill -9 50755 50756

or with

ps ax | grep simdeviceio | grep -v grep | awk '{print $1}' | xargs kill -9