Stencil: Jest 27 Upgrade Instructions

Stencil v2.13.0 now supports Jest v27, though upgrading is not mandatory, allowing users to continue using their current Jest version without any issues. For those choosing to upgrade to both Stencil v2.13.0 and Jest v27, it is advised to perform the upgrades in two separate steps to facilitate debugging: first upgrading Stencil, ensuring functionality, and then upgrading Jest. If issues arise during the Jest upgrade, it could be due to breaking changes in Jest v27, and users are encouraged to consult the Jest v27 announcement blog or the Stencil GitHub tracker for assistance. Notably, Stencil has made changes to ensure backward compatibility with older Jest versions, with jest-jasmine2 being the only supported test runner, and users should be aware that the first test run may be slower due to changes in Jest’s caching mechanism.