This file helps PHPUnit remember which tests previously failed, which can speed up your testing flow if you only re-run failed tests during development. This is useful for test-driven workflows in which you have configured tests to run automatically, such as on file save, and the same collection of tests is being run repeatedly.
It is also a good idea to add the cache file .phpunit.result.cache to
your .gitignore so that it does not end up being committed to your
repository.https://laravel-news.com/tips-to-speed-up-phpunit-tests
If you would prefer not to generate the file then you can run phpunit with the --do-not-cache-result option, as pointed out by @Slack Undertow in the comments. This might be desired when running tests as part of a build pipeline, for example. Or, as @codekandis pointed out, the same option is available as the cacheResult attribute in phpunit.xml.