Units are the smallest testable parts of software. The workflow patterns we use for testing TYPO3´s core have evolved over time and unit testing became an integral part quite a few years ago. This was after experiencing rather strange issues when first integrating the scheduler into the core.
Developing a successful and strong software requires a decent development platform with specific hardware, third-party software and parallelization of jobs. An efficient communication between this setup and other parts of the system ensures that processes run smoothly and swiftly.
Automatic testing is integrated into the process of developing TYPO's core. Every patch version that is pushed to the review system goes through a standard process and multiple verification ensures that the software conforms to requirements.