Ya’ll have it so easy with the tools that come with Xcode 7 to enable high quality code. Back in the day, Apple didn’t even recognize automated testing during WWDC (though tools were available in Xcode). It wasn’t until 2013 that a dedicated session to automated testing made the WWDC agenda. For posterity, go take a look:
WWDC 2013 – Testing in Xcode 5
or if you prefer, you can read it here.