In 1998, the Swiss company Sen:te developed OCUnit, a testing framework for Objective-C (hence, the OC prefix). OCUnit was a port of SUnit, a testing framework that Kent Beck had written for Smalltalk in 1994.
With Xcode 2.1, Apple added OCUnit to Xcode. One reason for this step was that they used it to develop Core Data at the same time that they developed Tiger, the OS with which Core Data was shipped. Bill Bumgarner, an Apple engineer, wrote this later in a blog post: