test: deflake user timing WPT assertions

The fixed 20 ms tolerance in mark.any.js can fail when execution pauses
between creating a mark and reading the clock. Adapt the test in memory
to check the mark timestamp against readings before and after mark().
Keep the vendored fixture and subtest names unchanged.

Apply script modifiers to worker entry scripts as well so the check
covers both WPT globals, and remove the suite-wide flaky expectation.

Signed-off-by: Filip Skokan <panva.ip@gmail.com>
Assisted-by: Codex
PR-URL: #66036
Backport-PR-URL: #66233
Fixes: #40449
Refs: #41203
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>

Author: panva

test/parallel/test-common-wpt-script-modifier.js

@@ -0,0 +1,35 @@
+'use strict';
+
+const common = require('../common');
+const assert = require('assert');
+const fixtures = require('../common/fixtures');
+const { spawnSync } = require('child_process');
+
+if (process.env.NODE_TEST_WPT_MODIFIER_PROBE === '1') {
+  const { WPTRunner } = require('../common/wpt');
+  const runner = new WPTRunner('html/webappapis/atob');
+  runner.setScriptModifier(common.mustCall((script) => {
+    assert.strictEqual(script.filename,
+                       fixtures.path('wpt', 'html/webappapis/atob', 'base64.any.js'));
+    script.filename += '.modified';
+    script.code = `test(() => {
+      assert_true(new Error().stack.includes(${JSON.stringify(`${script.filename}:`)}));
+    }, 'modified script retains its filename');`;
+  }));
+  runner.runJsTests();
+} else {
+  // eslint-disable-next-line no-unused-vars
+  const { WPT_REPORT, ...env } = { ...process.env, NODE_TEST_WPT_MODIFIER_PROBE: '1' };
+  const result = spawnSync(process.execPath, [__filename, 'base64.any.js'], {
+    env,
+    encoding: 'utf8',
+    timeout: common.platformTimeout(10_000),
+  });
+  const { error, status, stdout, stderr } = result;
+  assert.ifError(error);
+  assert.strictEqual(status, 0, stdout + stderr);
+  const results = stdout.split('\n').filter((line) => line.startsWith('[PASS]'));
+  assert.deepStrictEqual(results, [
+    '[PASS] modified script retains its filename',
+  ]);
+}

test/wpt/test-user-timing.js

@@ -1,9 +1,31 @@
 'use strict';
 
+const assert = require('assert');
+const { basename } = require('path');
 const { WPTRunner } = require('../common/wpt');
 
 const runner = new WPTRunner('user-timing');
 
 runner.pretendGlobalThisAs('Window');
 
+runner.setScriptModifier((script) => {
+  if (basename(script.filename) !== 'mark.any.js') return;
+
+  // A scheduling pause between mark() and now() can exceed any fixed
+  // tolerance. Check that the mark falls between the surrounding clock
+  // readings instead, leaving the upstream fixture unchanged.
+  // https://github.com/nodejs/node/issues/40449
+  function replace(from, to) {
+    assert(script.code.includes(from), `Unexpected contents of ${script.filename}`);
+    script.code = script.code.replaceAll(from, to);
+  }
+
+  replace('var expectedTimes = new Array();',
+          'var beforeTimes = [];\nvar expectedTimes = new Array();');
+  replace('self.performance.mark("mark");',
+          'beforeTimes.push(self.performance.now());\n    self.performance.mark("mark");');
+  replace('assert_approx_equals(entries[index].startTime, expectedTimes[index], testThreshold);',
+          'assert_between_inclusive(entries[index].startTime, beforeTimes[index], expectedTimes[index]);');
+});
+
 runner.runJsTests();

test/wpt/wpt.status

@@ -5,8 +5,6 @@ prefix wpt
 # sample-test                        : PASS,FLAKY
 
 [true] # This section applies to all platforms
-# https://github.com/nodejs/node/issues/40449
-test-user-timing: PASS,FLAKY
 
 [$system==win32]