[uplift] chore: Vitest 5 in Node and browsers, remove test cruft

.github/workflows/ci.yml

@@ -40,15 +40,66 @@ jobs:
           cache: 'pnpm'
       - name: Install dependencies
         run: pnpm install --frozen-lockfile
+      # For the `browser` test project (Vitest browser mode).
+      - name: Install browsers
+        if: matrix.os == 'ubuntu-latest'
+        run: pnpm exec playwright install --with-deps --only-shell chromium firefox webkit
       - name: Check
         if: matrix.os == 'ubuntu-latest'
         run: pnpm check
+      # Node project only (v8 coverage doesn't work in Firefox or WebKit).
+      # Reported in the job summary, not gated: Check gates on the tests.
+      - name: Coverage
+        if: matrix.os == 'ubuntu-latest'
+        continue-on-error: true
+        run: pnpm test --project node --coverage
+      - name: Coverage summary
+        if: always() && matrix.os == 'ubuntu-latest'
+        run: |
+          {
+            echo '### Coverage'
+            if [ -f coverage/summary.txt ]; then
+              echo '```'
+              cat coverage/summary.txt
+              echo '```'
+            else
+              echo 'No coverage summary (the Coverage step failed or was skipped).'
+            fi
+          } >> "$GITHUB_STEP_SUMMARY"
       # Report only: adds the size table to the job summary, never fails.
       - name: Size
         if: always() && matrix.os == 'ubuntu-latest'
         run: pnpm size --base HEAD^1
-      # Format, lint and the packed tarball don't depend on the OS, so Windows
-      # only runs the tests.
+      # Format, lint, the packed tarball and the browsers don't depend on the
+      # OS, so Windows only runs the Node tests.
       - name: Test
         if: matrix.os == 'windows-latest'
-        run: pnpm test
+        run: pnpm test --project node
+
+  # The lockfile has React 19 and Preact 11, which the test job covers. This
+  # job runs the Node tests on the oldest versions we check: exactly React
+  # 18.0.0, and the newest Preact 10 (`preact/compat`). The library doesn't
+  # depend on either; this guards its `$$typeof` / `_owner` handling.
+  older-renderers:
+    name: Test (React 18.0.0, Preact 10)
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read # to check out repo (actions/checkout)
+    steps:
+      - uses: actions/checkout@v7
+        with:
+          persist-credentials: false
+      - uses: pnpm/action-setup@ea17c68df8912ef543352723c149a84f56e3d413 # v6.1.0
+      - uses: actions/setup-node@v7
+        with:
+          node-version-file: '.nvmrc'
+          cache: 'pnpm'
+      - name: Install dependencies
+        run: pnpm install --frozen-lockfile
+      # Changes the working tree only; nothing is committed.
+      - name: Install React 18.0.0 and Preact 10
+        run: |
+          pnpm add --save-dev react@18.0.0 react-dom@18.0.0 preact@^10
+          node -e 'for (const [p, v] of [["react", "18.0.0"], ["react-dom", "18.0.0"], ["preact", "10."]]) { const got = require(`${p}/package.json`).version; console.log(`${p} ${got}`); if (!got.startsWith(v)) throw new Error(`${p} is ${got}, expected ${v}`); }'
+      - name: Test
+        run: pnpm test --project node

.gitignore

@@ -10,8 +10,6 @@ yarn.lock
 
 # Test output
 coverage/
-.nyc_output/
-test/typescript/*.js
 
 # Output of `npm pack` / `pnpm pack`
 *.tgz

.oxlintrc.json

@@ -27,9 +27,6 @@
   "overrides": [
     {
       "files": ["test/**"],
-      "env": {
-        "mocha": true
-      },
       "globals": {
         "document": "readonly",
         "Element": "readonly"

CONTRIBUTING.md

@@ -53,53 +53,52 @@ included. For an urgent security fix that's newer than that, add the package to
 **TL; DR:** － Everything you normally need to run is aggregated into:
 
 ```sh
-# Format, lint, then all tests
+# Format, lint, types, all tests, then the packed package
 $ pnpm run check
 $ pnpm run benchmark
 ```
 
-(We use `builder` to parallelize things, so tasks may output in different
-orders)
-
 ### Testing
 
-We write one set of tests located in:
-
-- `test/node/**.spec.js`
+We test with [Vitest](https://vitest.dev/). One set of specs, `test/*.spec.mjs`,
+runs in two projects (`vitest.config.mts`):
 
-that run in two very different scenarios (below). Most generic test cases come
-from `fast-deep-equal`, vendored unchanged in `test/fixtures/fast-deep-equal/`
-(see its README).
+- `node`: Node, with [jsdom](https://github.com/jsdom/jsdom) for the specs
+  that need a DOM.
+- `browser`: [Vitest browser mode](https://vitest.dev/guide/browser/) in
+  headless Chromium, Firefox and WebKit, through Playwright.
 
-#### Node
+Most generic test cases come from `fast-deep-equal`, vendored unchanged in
+`test/fixtures/fast-deep-equal/` (see its README). Our own cases (React
+elements, custom behavior) are in `test/fixtures/index.mjs`, and
+`test/react.spec.mjs` renders real React and Preact (`preact/compat`)
+components.
 
-The tests are natively run in `node` (hence why they are located in `tests/node`
-to begin with) without any transpilation or "build". You can run them with:
+Install the browsers once (and again when Playwright is updated):
 
 ```sh
-# Single run
-$ pnpm run test-node
-
-# Persistent watch
-$ pnpm run test-node --watch
+$ pnpm exec playwright install --only-shell chromium firefox webkit
 ```
 
-#### Browsers
+```sh
+# All projects
+$ pnpm test
 
-The same tests are then imported and built with `webpack` to a test bundle that
-can be run in arbitrary browsers. CI runs them in headless Chrome on Linux and
-Windows (GitHub Actions).
+# Node only, or one browser
+$ pnpm test --project node
+$ pnpm test --project "browser (firefox)"
 
-To run the browser tests on your machine (note: you must already have the
-browser you're running installed):
+# Watch mode
+$ pnpm vitest --project node
 
-```sh
-# Default: headless chrome
-$ pnpm run test-browser
-# Example: real Chrome + Firefox + Safari
-$ pnpm run test-browser --browsers Chrome,Firefox,Safari
+# Coverage (Node only; v8 coverage doesn't work in Firefox or WebKit)
+$ pnpm test --project node --coverage
 ```
 
+CI runs every project on Linux and adds the coverage summary to the job
+summary. It runs the Node project on Windows, and on React 18.0.0 with Preact
+10 (the lockfile has React 19 and Preact 11).
+
 ### Types
 
 `pnpm types:check` type-checks `index.js` from its JSDoc and checks that the declarations it emits match `index.d.ts`. `pnpm pack:check` then compiles the type probe in `test/types/` against the packed package, as a CommonJS (`.cts`) and an ES module (`.mts`) consumer. Add a case there for any usage the types must keep supporting.

benchmark/index.js

@@ -1,6 +1,6 @@
 'use strict';
 
-const tests = require('../test/node/tests');
+const tests = require('../test/fixtures/index.mjs');
 const Benchmark = require('benchmark');
 
 const correctnessTests = [];

package.json

@@ -5,18 +5,14 @@
   "main": "index.js",
   "typings": "index.d.ts",
   "scripts": {
-    "preversion": "pnpm check",
     "check": "pnpm format && pnpm lint && pnpm types:check && pnpm test && pnpm pack:check",
     "benchmark": "node benchmark",
     "format": "oxfmt --check",
     "format:fix": "oxfmt",
     "lint": "oxlint --report-unused-disable-directives-severity=error",
     "lint:fix": "oxlint --report-unused-disable-directives-severity=error --fix",
     "types:check": "node scripts/types-check.mjs",
-    "test-browser": "karma start test/browser/karma.conf.js",
-    "test-node": "mocha \"test/node/*.spec.js\"",
-    "test-node-cov": "nyc mocha \"test/node/*.spec.js\"",
-    "test": "builder concurrent --buffer test-node-cov test-browser",
+    "test": "vitest run",
     "changeset": "changeset",
     "pack:check": "node scripts/pack-check.mjs",
     "size": "node scripts/size.mjs"
@@ -42,55 +38,27 @@
   "packageManager": "pnpm@12.16.0",
   "devDependencies": {
     "@arethetypeswrong/cli": "0.18.5",
-    "@babel/core": "^7.21.0",
-    "@babel/preset-env": "^7.20.2",
     "@changesets/changelog-github": "^1.0.1",
     "@changesets/cli": "^3.0.3",
-    "@testing-library/dom": "^9.0.1",
-    "@testing-library/preact": "^3.2.3",
-    "@types/node": "^18.15.0",
     "@types/react": "^19.3.0",
-    "assert": "^2.0.0",
-    "babel-loader": "^9.1.2",
+    "@vitest/browser-playwright": "^5.0.5",
+    "@vitest/coverage-v8": "^5.0.5",
     "benchmark": "^2.1.4",
-    "builder": "^5.0.0",
-    "core-js": "^3.29.0",
     "fast-deep-equal": "3.1.3",
-    "jsdom": "^21.1.0",
-    "jsdom-global": "^3.0.2",
-    "karma": "^6.4.1",
-    "karma-chrome-launcher": "^3.1.1",
-    "karma-firefox-launcher": "^2.1.2",
-    "karma-mocha": "^2.0.1",
-    "karma-mocha-reporter": "^2.2.5",
-    "karma-safari-launcher": "^1.0.0",
-    "karma-webpack": "^5.0.0",
+    "jsdom": "^30.1.3",
     "lodash": "^4.17.10",
-    "mocha": "^11.8.0",
     "nano-equal": "^2.0.2",
-    "nyc": "^15.1.0",
     "oxfmt": "0.75.0",
     "oxlint": "1.90.0",
-    "preact": "^10.13.1",
-    "process": "^0.11.10",
+    "playwright": "^1.64.1",
+    "preact": "^11.1.1",
     "publint": "0.3.25",
-    "react": "^18.2.0",
-    "react-test-renderer": "^18.2.0",
+    "react": "^19.3.1",
+    "react-dom": "^19.3.1",
     "shallow-equal-fuzzy": "0.0.2",
-    "sinon": "^15.0.1",
     "terser": "5.51.2",
     "typescript": "7.0.2",
-    "webpack": "^5.76.0"
-  },
-  "nyc": {
-    "exclude": [
-      "**/test/**",
-      "node_modules"
-    ],
-    "reporter": [
-      "lcov",
-      "text-summary"
-    ]
+    "vitest": "^5.0.5"
   },
   "files": [
     "index.js",