PHPUnit, the popular PHP testing framework, has traditionally run tests one-at-a-time due to their fast nature. However, with the increasing use of Selenium tests for end-to-end system testing, which are slower and more resource-intensive, running tests sequentially becomes a bottleneck in delivering new code quickly. To address this issue, PHPUnit's parallelism solution was developed, allowing users to run tests in parallel using a command line parameter or a custom TestCase class attribute. The solution is fully cross-platform and has been contributed to PHPUnit core as of November 2011, with a preview version available for testing. However, due to changes in the project's direction, the internal parallelism code will be rewritten by Sebastian, the founder and maintainer, which may delay its release until April 2013.