test(react-context-selector): add cypress regression for eager-bailout (React 18)#36033
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layershifter merged 6 commits intomasterfrom Apr 24, 2026
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…t (React 18) Adds cypress component-testing scaffold (matches `@fluentui/workspace-plugin` cypress-component-configuration generator output) to the package and a regression test for the `useContextSelector` eager-bailout pitfall described in the context-selector-tearing RFC. The bug is not observable via jest + `@testing-library/react`: React runs the function body and then discards the render via `bailoutOnAlreadyFinishedWork`, so no commit happens and `useEffect` never fires. The cypress test uses an in-render counter on `window` to catch the discarded-render leak (item 1's render count grows from 3 to 4 on click 3). The glitch is React-18-only (React 19 relaxed the eager-bailout precondition), so the assertion is meaningful under `nx run react-context-selector:test-rit--18--e2e`. Expected to be RED on master (v1 hook) and GREEN once #36002 lands. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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…en retries Cypress retries a failing test up to 5 times by default and reuses the component iframe window across retries. The render counter on `window` was accumulating across attempts (5 attempts × 1 mount-render = 5), making the very first post-mount assertion fail before the actual regression check was reached. Reset the counter in `beforeEach` so each attempt sees an absolute, not-cumulative count.
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Pull request demo site: URL |
… dimensions The previous test used a bare div wrapping empty divs which had 0 height, so cy.click() on the provider failed its visibility check. Wrap in a button (so clicks pass visibility) and render visible text content in items.
… of window Replace window.__useContextSelectorRenderCounts__ with a module-level RENDER_COUNTS object. Simpler — no window type munging, no lazy init. Reset via in-place mutation in beforeEach so cy.wrap(RENDER_COUNTS).should(...) sees the mutation on each cypress retry.
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dmytrokirpa
approved these changes
Apr 23, 2026
jurokapsiar
approved these changes
Apr 24, 2026
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Summary
@fluentui/react-context-selectorsrc/useContextSelector.cy.tsx- a 3-click cycling regression test for theuseStateeager-bailout pitfall documented in RFC: useContextSelector() amend with Option D (Relay pattern) #36001Why cypress and not jest?
The bug: React runs the function component body then discards the JSX via
bailoutOnAlreadyFinishedWork. The DOM does not change — but the function already ran. A commit-timeduseEffectcannot observe this, so jest/jsdom tests pass even when the bug is present.Expected CI behavior
test-rit--18--e2eexpected to be 🔴 This is intentional — it proves the test catches the bug.Companion work:
🤖 Generated with Claude Code