Jest 27 was released with numerous bug fixes and improvements. The most significant are: 1. New test default test runner called `jest-circus` which replaced old Jasmine 2.0 code and made Jest faster. 2. Native ESM support. 3. `transform` is asynchronous now and supports transpilation through esbuild, vite. 4. Default test environment was changed from `jsdom` to `node`. 5. The modern fake timers implementation is the default now. After migration to Jest 27 we need to migrate to Jest 28 as this version is considered as LTS. **References:** - https://jestjs.io/blog/2021/05/25/jest-27 - https://github.com/facebook/jest/blob/main/CHANGELOG.md#2700