In OS X 10.10 (Yosemite Beta), How do I Test Using iOS 6.1 Simulator?

As far as I have experienced, The iPhone simulator always have this kind of issue on every update of OS X, since the core of iPhone simulator is using the core of OS X, and it only support the latest two version. That is,

10.10 -> iOS 7, iOS 8.

10.9 -> iOS 6, iOS 7.

Meanwhile, Xcode obviously only support for downloading the latest two version simulator, which means you can get iOS 6 simulator in Xcode 5, but not in Xcode 6.

However you can get the old simulator by copy/paste the old SDKs into the correct folder, but this still follows the OSX-iOS relation. That is, if you have the iOS 6 simulator SDK, you can run the iOS 6 simulator on OSX 10.9, but not OSX 10.10.

iOS Simualtor runtimes older than iOS 7.0 will not work with Xcode 6.iOS Simulator runtimes older than iOS 7.1 will not work on OS X Yosemite.

Older versions of the iOS Simulator runtime cannot be made to work with Xcode 6 nor on OS X Yosemite without significant changes to those legacy runtimes.

You can still build your apps to support older iOS versions by setting an older deployment target, but you will not be able to test them on a simulated device running on OS X Yosemite. You can test on a physical device running iOS 6.1, or you can run Xcode 5.1.1 in OS X Mavericks to test your project in the older simulator.