Test: Update Vitest to version 5

[ciampo]

What?

Follow up to #80855.

Updates Gutenberg's test infrastructure to Vitest 5, including the related Browser, Testing Library, jest-dom, and flakiness reporter dependencies. This is a standalone change based on trunk.

Why?

Vitest 5 requires Node 22.12 or later. Gutenberg now requires Node 24, so the repository can adopt the current major release.

This PR applies the migration changes needed by current consumers and leaves optional configuration and performance experiments for follow-ups.

How?

• Aligns vitest and @vitest/browser-playwright at 5.0.0. It also updates Testing Library React to 16.3.3, jest-dom to 7.0.1, and @flakiness/vitest to 1.9.2.
• Migrates custom matcher types, runner-specific jest-dom setup, the removed describe.sequential API, and changed snapshot title formatting.
• Keeps clearMocks: false because mockReset: true already performs the same call-history cleanup and also resets implementations.
• Ignores Vitest's .vitest artifact directory.
• Disconnects useResizeObserver on unmount. Vitest 5's stricter error handling exposed a queued callback running during jsdom teardown.

Complete release span and dependency versions

• vitest 4.1.11 to 5.0.0: 5.0.0
• @vitest/browser-playwright 4.1.10 to 5.0.0: 4.1.11, 5.0.0
• @testing-library/react 16.3.2 to 16.3.3: 16.3.3
• @testing-library/jest-dom 6.9.1 to 7.0.1: 6.10.0, 7.0.0, 7.0.1
• @flakiness/vitest 1.9.0 to 1.9.2: 1.9.1, 1.9.2

Vitest's transitive Browser, mocker, UI, and runtime packages use the same 5.0.0 monorepo release. @vitest/ui is new to the lockfile, so it has no earlier resolved version.

Notable upstream changes

• Runtime requirements. Vitest 5 requires Node 22.12+ and Vite 6.4+. Gutenberg uses Node 24 and Vite 8.2.2. This affects development tests only.
• Matcher types and removed APIs. Gutenberg's shared matcher environment and Interactivity tests used the changed Matchers<R, T> type. One infrastructure test used describe.sequential. Both required migration. TypeScript and the full suite pass.
• Stricter assertions and errors. No assertion or hoisted-mock rewrites were needed. The stricter runner did expose useResizeObserver work continuing after unmount, which this PR fixes and covers with a regression test.
• clearMocks by default. Gutenberg already enables the stronger mockReset. The explicit clearMocks: false avoids a redundant cleanup pass, and an infrastructure test documents the choice.
• Browser Mode. Gutenberg does not use the changed custom-command or browser.api contracts. The Gutenberg Browser project and all 833 Storybook Browser tests pass. .vitest is ignored for new failure artifacts.
• Optional features. Nested projects, shared Vite servers, the filesystem module cache, Temporal mocking, and new reports are not compatibility requirements. Gutenberg has no Temporal consumer or Vitest bench import. The useful experiments are listed below.
• Related dependencies. Testing Library React 16.3.3 fixes re-entrant act() handling. jest-dom 7's Node and @testing-library/dom requirements are satisfied, and 7.0.1 declares Vitest as an optional peer. The flakiness patches correct Vitest stdio and .fails reporting. These changes affect tests and reporting only.

The review also covered the complete Vitest migration guide and Vitest 5 release highlights.

Known compromise

@storybook/addon-vitest 10.5.9 still declares Vitest 3/4 peers, so npm ls reports the Vitest 5 packages as invalid. The clean install, production build, static Storybook build, and all 833 Storybook Browser tests pass with the unpatched addon. Removing it would remove Storybook's Vitest coverage, while a local metadata patch would only hide the warning. This PR keeps it unchanged while storybookjs/storybook#36221 adds upstream support.

Performance

The same-head Node 24 comparison found no reproducible speed improvement. Four CI-shaped Node/jsdom shards were flat overall, and the three-run Storybook median was 0.4% slower. Vitest's shared-server optimization does not apply to Gutenberg's current project layout.

Measurements

Workload	Vitest 4	Vitest 5	Result
Four Node/jsdom shards, total	228.19 s	228.68 s	+0.2%
Four shards, critical path	59.49 s	62.40 s	+4.9%
Storybook Browser tests, median	102.60 s	102.97 s	+0.4%

Both versions used Node 24 and base commit b21da9b2199.

Follow-ups

Configuration, performance, and flake investigations

• Prototype nested Node/jsdom projects with inherited configuration and a shared Vite server. An initial experiment kept all 1,068 files and reduced one shard's two-run mean by about 6.8%, but combining the integration and Browser projects discovered zero integration tests.
• Re-test fsModuleCache. A warm-cache trial improved the median by about 4.7%, but worsened the mean, created about 93 MB of cache data, and does not support Browser Mode.
• Investigate the load-sensitive jest-console subprocess timeout under CI-shaped contention. It reached the five-second limit during loaded full runs, but passed 20 isolated repetitions and the final complete run. Profile Jest startup before changing the test or timeout.
• Consider injectCjsGlobals: false, Browser traces, and single-file HTML reports as separate hardening and diagnostics changes.
• Adopt Temporal mocking if Gutenberg begins testing Temporal behavior.

Testing Instructions

1. Install with Node 24 and run the dependency validation scripts.
2. Run the typecheck, production build, convention tests, routing tests, and complete Vitest suite.
3. Build Storybook and run its complete smoke suite.
4. Run npm ls vitest @vitest/browser @vitest/browser-playwright. The only invalid peers should be the documented Storybook addon ranges.

Verified locally with a clean install, build, typecheck, dependency checks, 35,749 passing Vitest tests, and 833 passing Storybook Browser tests.

Testing Instructions for Keyboard

Not applicable. This PR changes development dependencies and test infrastructure only.

Use of AI Tools

Codex helped audit upstream releases and migration guidance, inspect consumers, implement the changes, run verification and performance comparisons, and draft this description. The author reviewed the changes and conclusions against the repository and official upstream sources.

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Co-authored-by: ciampo <mciampini@git.wordpress.org>
Co-authored-by: manzoorwanijk <manzoorwanijk@git.wordpress.org>

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[github-actions]

🤖 PR meta 🤖

📦 Bundle size

Size Change: +23 B (0%)

Total Size: 8 MB

📦 View Changed

Filename	Size	Change
build/scripts/compose/index.min.js	11.7 kB	+23 B (+0.2%)

_{456acd0 Run}

⚡ Performance

Show the results

Client side metrics exclude the server response time.

front-end-block-theme

Metric	fcdc678	trunk	% Change
timeToFirstByte	57.5 ms +10.87% -6.26%	54.75 ms +11.32% -3.74%	5.02%
largestContentfulPaint	98 ms +6.12% -8.16%	92 ms +8.7% -8.7%	6.52%
lcpMinusTtfb	35.6 ms +24.58% -2.39%	33.8 ms +22.04% -5.77%	5.33%
wpBeforeTemplate	27.79 ms +20.69% -3.49%	26.29 ms +19.67% -1.22%	5.71%
wpTemplate	25.19 ms +3.06% -7.66%	23.57 ms +2.5% -3.52%	6.87%
wpTotal	53.41 ms +11.48% -6.14%	51.08 ms +10.73% -4.46%	4.56%
wpMemoryUsage	7.52 MB +0% -0%	7.48 MB +0% -0%	0.46%
wpDbQueries	17 +0% -0%	17 +0% -0%	0%

front-end-classic-theme

Metric	fcdc678	trunk	% Change
timeToFirstByte	42.3 ms +12.29% -3.9%	41.1 ms +4.62% -1.95%	2.92%
largestContentfulPaint	98 ms +6.12% -2.04%	96 ms +0% -4.17%	2.08%
lcpMinusTtfb	54.3 ms +3.04% -1.84%	53.3 ms +3.94% -3.47%	1.88%
wpBeforeTemplate	24.43 ms +14.94% -4.67%	23.22 ms +3.96% -0.73%	5.21%
wpTemplate	14.55 ms +6.46% -3.64%	14.3 ms +3.36% -2.59%	1.75%
wpTotal	39.2 ms +12.88% -4.39%	38.01 ms +5.08% -2.21%	3.13%
wpMemoryUsage	5.51 MB +0% -0%	5.47 MB +0% -0%	0.64%
wpDbQueries	14 +0% -0%	14 +0% -0%	0%

media-processing

Metric	fcdc678	trunk	% Change
mediaProcessingJpeg	412.75 ms +2.88% -0.73%	413.74 ms +0.59% -0.92%	-0.24%
mediaProcessingAvif	6164.88 ms +0.43% -0.11%	6179.01 ms +0.19% -0.22%	-0.23%
mediaProcessingJpegToAvif	4301.03 ms +0.59% -0.16%	4302.01 ms +0.3% -0.23%	-0.02%

media-upload

Metric	fcdc678	trunk	% Change
jpegUploadProcessing	1440.25 ms +34.98% -1.28%	1422.59 ms +1.6% -0.55%	1.24%
pngUploadProcessing	201.85 ms +2.24% -3.42%	200.4 ms +5.28% -1.37%	0.72%
largeJpegUploadProcessing	1411.57 ms +0.31% -0.41%	1414.77 ms +0.47% -0.35%	-0.23%
multipleImageUploadProcessing	1545.61 ms +1.53% -2.07%	1571.48 ms +1.33% -1.42%	-1.65%

post-editor

Metric	fcdc678	trunk	% Change
serverResponse	311.11 ms +16.87% -1.92%	335.17 ms +3.3% -6.68%	-7.18%
firstPaint	207.79 ms +24.18% -16.58%	179.58 ms +19.38% -10.74%	15.71%
domContentLoaded	1022.47 ms +3.9% -0.63%	1027.92 ms +1.31% -0.73%	-0.53%
loaded	1023.56 ms +3.9% -0.62%	1029.04 ms +1.32% -0.72%	-0.53%
firstContentfulPaint	354.35 ms +0.28% -1.55%	347.74 ms +2.22% -4.21%	1.9%
firstBlock	2763.47 ms +2.5% -1.1%	2766.73 ms +0.77% -0.59%	-0.12%
type	13.54 ms +4.95% -6.57%	13.25 ms +6.11% -1.43%	2.19%
typeWithoutInspector	13.33 ms +4.58% -6.23%	13.17 ms +5.01% -5.09%	1.21%
typeWithTopToolbar	15.25 ms +2.1% -4.92%	16.72 ms +4.43% -6.88%	-8.79%
typeContainer	7.56 ms +16.27% -3.7%	7.95 ms +11.32% -7.04%	-4.91%
focus	66.06 ms +14.58% -9.11%	67.01 ms +4.92% -6.92%	-1.42%
firstFocus	142.44 ms +0% -0%	148.48 ms +0% -0%	-4.07%
selectAll	464.81 ms +0.35% -1.8%	456.82 ms +3.93% -2.59%	1.75%
listViewOpen	55.8 ms +10.41% -10.84%	57.56 ms +4.99% -11.5%	-3.06%
inserterOpen	21.21 ms +10.14% -9.24%	20.43 ms +2.64% -7.34%	3.82%
inserterHover	3.43 ms +8.75% -6.41%	3.54 ms +15.25% -7.06%	-3.11%
inserterSearch	7.53 ms +8.9% -5.71%	7.26 ms +10.33% -2.89%	3.72%
loadPatterns	527.98 ms +5.51% -3.25%	543.33 ms +2.38% -3.71%	-2.83%
wpTotal	302.26 ms +17.32% -1.91%	326.2 ms +3.52% -6.82%	-7.34%
wpMemoryUsage	13.05 MB +0% -0%	13.02 MB +0% -0%	0.28%
wpDbQueries	54 +0% -0%	54 +0% -0%	0%

site-editor

Metric	fcdc678	trunk	% Change
serverResponse	310.07 ms +4.68% -3.62%	325.42 ms +1.93% -2.73%	-4.72%
firstPaint	204.68 ms +64.26% -12.69%	191.37 ms +13.15% -16.31%	6.96%
domContentLoaded	1094.84 ms +0.78% -0.4%	1091.5 ms +1.13% -1.23%	0.31%
loaded	1095.88 ms +0.79% -0.39%	1092.63 ms +1.12% -1.24%	0.3%
firstContentfulPaint	345.12 ms +7.79% -2.58%	352 ms +1.64% -4.27%	-1.95%
firstBlock	3427.83 ms +1.44% -0.4%	3432.76 ms +0.52% -0.67%	-0.14%
type	13.44 ms +4.61% -5.65%	13.53 ms +5.47% -7.46%	-0.67%
navigate	76.86 ms +18.62% -14.42%	67.64 ms +17.42% -2.57%	13.63%
loadPatterns	1070.77 ms +23.27% -3.44%	1107.34 ms +17.83% -2.22%	-3.3%
loadPages	1104.57 ms +1.52% -0.81%	1083.47 ms +3.48% -2.7%	1.95%
wpTotal	301.67 ms +4.87% -3.74%	317.02 ms +1.94% -2.83%	-4.84%
wpMemoryUsage	12.06 MB +0% -0%	12.03 MB +0% -0%	0.3%
wpDbQueries	44 +0% -2.27%	43.5 +1.15% -1.15%	1.15%

_{456acd0 Run}

[manzoorwanijk]

The change looks straighforward if the CI is happy.

[ciampo]

@aduth another fix!