Speed up unit tests by reusing Vitest workers - #1317
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charlespwd
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October 1, 2026 12:50
karreiro
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Thank you, @charlespwd 🔥
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In this PR
Reuse each Vitest worker across test files instead of starting a fresh process for every file. In local profiling, this cuts the five CI unit-test commands from about 100 seconds to about 11 seconds.
Problem
The Vitest 4 migration kept the suite at one worker but lost the old
singleForkbehavior. The suite now starts hundreds of child processes sequentially, while the test bodies themselves take only a few seconds.Solution
Run the root and Prettier suites with
isolate: falseso their files share one process and module cache.Five root tests depend on a fresh module graph, so they stay in a small isolated Vitest project. The shared setup also installs its unhandled-rejection logger once per worker process, including filtered runs and collection failures.