Jest is slow in part because it fully isolates each test file from every other test file. For small, highly-experienced teams those guardrails don't provide muc

Jest is slow in part because it fully isolates each test file from every other test file. For small, highly-experienced teams those guardrails don't provide much benefit. For large teams, that isolation is essential to prevent cross-test contamination. Another reason Jest is slow is due to how it's usually configured to build code using Babel or tsc. Like vitest, you can configure Jest to use esbuild which makes it much faster than using Babel or tsc. I am not a big Jest fan, but it seems like the most pragmatic test runner when you have 100+ engineers working on a project.