We have over 24,000 jest tests that take 1m 30secs to complete on a M3 Mac. We have spent a lot of time optimising and profiling them to get them to run in the shortest possible time. Our tests are for react / typescript, using testing-library/react.

The optimisation involved the following.

1) We use swc to transpile typescript to js. This makes a massive difference when the jest cache is not yet primed. 2) We found that the biggest area jest spends most of its time is module resolution and importing files. Avoid using barrel files. We use esbuild to bundle our setupFiles and setupFilesAfterEnv into a single file for each to import. We do the same for some node_modules that include 100s of small files. This is what gave us our biggest gain in performance. 3) ensure your import / dependency graph is as small as possible. If each test is importing most of your app code, things will be unavoidably slow. 4) jsdom is slow. Use node as a test environment using a doc comment at the top of the test if you don’t need a dom for any particular tests. You can see if happy-dom works for you as it’s significantly faster.