René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Support `concurrency` when `--experimental-test-isolation` is set to `'none'`","articleBody":"### What is the problem this feature will solve?\n\nIt would be nice to be able to run multiple \"workers\" when using the `none` test isolation mode.\r\n\r\nToday, according to the docs, when `--experimental-test-isolation` is set to `'none'`, it implies 1 concurrency: https://github.com/nodejs/node/blob/f270462c09ddfd770291a7c8a2cd204b2c63d730/doc/api/cli.md#L2252-L2264\r\n\r\nHowever, `mocha` another test runner that does not isolate tests, does accept a concurrency flag: https://mochajs.org/#parallel-tests\n\n### What is the feature you are proposing to solve the problem?\n\nWe're looking to move off of `jest` because its test module isolation is extremely slow. We love the idea of using the node-native test runner with isolation disabled, instead of adopting another third-party framework like `mocha`.\r\n\r\nHowever, we'd need to write some custom code (e.g., using [`parallel`](https://www.gnu.org/software/parallel/)) to spin up `n` concurrent, isolation-disabled tests to effectively utilize all the cores available on our CI machine.\r\n\r\nThe docs and other recent comments all indicate that when `--experimental-test-isolation` is set to `'none'`, concurrency must be `1`. However, I couldn't find the reasoning in [the original PR](https://github.com/nodejs/node/pull/53927) or [issue](https://github.com/nodejs/node/issues/51548).\r\n\r\nThere's probably a good reason for this but, as someone not intimately familiar with the implementation, it's not obvious to me why we wouldn't be able to run non-isolated tests concurrently, like in `mocha`.\n\n### What alternatives have you considered?\n\nI could probably use a tool like [`parallel`](https://www.gnu.org/software/parallel/) to spin up multiple calls to `node --test`. However, this would require me to also write code to split up all the test files between the parallel runs, etc.","author":{"url":"https://github.com/blimmer","@type":"Person","name":"blimmer"},"datePublished":"2024-11-20T22:08:01Z","url":"https://github.com/nodejs/node/issues/55939"}