Summary & Key Takeaways ​

• Mock functions now support whenCalledWith to configure return values based on specific arguments.
• jest.retryTimes() can now be applied to entire describe blocks, rerunning all hooks and tests.
• The file watcher for non-Watchman environments has been rewritten using @parcel/watcher.
• fdir replaces hand-rolled directory recursion in the crawler.
• The release touches jest-runtime, jest-resolve, and jest-haste-map extensively.
• Argument slots for whenCalledWith accept literals or asymmetric matchers.

Our Commentary ​

This is a genuinely big release for Jest, despite being a minor version. whenCalledWith is a game-changer for mocking complex scenarios, and describe-level retries will save so much headache for flaky integration tests. I'm also curious about the new file watcher; performance improvements there are always welcome. It's a solid set of features that will make testing more robust and flexible.