Xcode server, bots, continuous integration, and unit-testing on the simulator
I had a similar issue that was solved by changing the Xcode Bot to run only 1 of the latest version simulator (Xcode 6.3.1 and iOS 8.3) and force quitting all the simulator related processes on my server.
Just log onto your server and launch Activity Monitor, then go to the CPU tab, now search for "simulator", you should see a few results, just force quit all of them (even ones belonging to _xcsbuildd). Here are examples of Process Names I have:
- com.apple.CoreSimulator.CoreSimulatorService
- iOS Simulator
- SimulatorBridge
- CoreSimulatorBridge