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[test] Stop leaking mocked performance clocks into later test files - #37379
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Test files running in the Node.js Jest environment share the worker
process's `performance` object, because `jest-environment-node` installs
it by reference rather than by copy. When a test mocked the clock with
`Object.defineProperty(performance, 'now', ...)`, the mutation hit the
shared object and was never undone, since Jest only restores
`jest.spyOn` mocks when a file's runtime is torn down. Every subsequent
test file in the same worker then observed the fake clock, including
jsdom-based files, whose `performance.now()` subtracts a window-creation
timestamp from the shared object's `now()`.
This change switches the six affected test files to
`jest.spyOn(performance, 'now')` and
`jest.spyOn(performance, 'timeOrigin', 'get')`, which Jest restores
automatically at teardown. `ReactFlightDOMEdge-test.js` runs in jsdom
and therefore did not leak, but it used the same pattern and is
converted for consistency. The leak is a suspect for the flaky
`{"time":NaN}` Flight serialization failure seen in CI, since a leaked
clock whose `now()` returns a non-number propagates NaN into the
timing rows the Flight server serializes.
Co-Authored-By: Claude Code (kimi-k3[1m]) <noreply@anthropic.com>Comparing: 373d35e...c71633e Critical size changesIncludes critical production bundles, as well as any change greater than 2%:
Significant size changesIncludes any change greater than 0.2%: (No significant changes) Generated by sizebot against c71633e |
eps1lon
marked this pull request as ready for review
August 26, 2026 06:50
unstubbable
approved these changes
Aug 26, 2026
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Test files running in the Node.js Jest environment share the worker process's
performanceobject, becausejest-environment-nodeinstalls it by reference rather than by copy. When a test mocked the clock withObject.defineProperty(performance, 'now', ...), the mutation hit the shared object and was never undone, since Jest only restoresjest.spyOnmocks when a file's runtime is torn down (jest-runtime'steardown()callsrestoreAllMocks()). Every subsequent test file in the same worker then observed the fake clock, including jsdom-based files, whoseperformance.now()subtracts a window-creation timestamp from the shared object'snow().This change switches the six affected test files to
jest.spyOn(performance, 'now')andjest.spyOn(performance, 'timeOrigin', 'get'), which Jest restores automatically at teardown.ReactFlightDOMEdge-test.jsruns in jsdom and therefore did not leak, but it used the same pattern and is converted for consistency.This change is mostly for test hygiene. Was discovered while investigating a flaky
{"time":NaN}serialisation bug (e.g. https://github.com/react/react/actions/runs/32878999825/job/97903912119)