I just downloaded and installed Xcode 5 GM seed. I removed the previous Xcode (DP5). When I open my project, select "iPhone Retina (4-inch 64 bit)" and type Command-U to run my SenTeskingKit unit tests, Xcode invariably complains:
"Simulator in Use - The Simulator can't be launched because it is already in use."
I have run xcode-select to point to the new Xcode, restarted my MacBookPro, and made sure there are no other iPhone sim processes running under the Activity Monitor.