From d6fdfbb3858e478e75ab9e6f26cb0710735b14e0 Mon Sep 17 00:00:00 2001
From: Moshe Atlow <moshe@atlow.co.il>
Date: Tue, 19 May 2026 16:56:05 +0300
Subject: [PATCH] test_runner: dont buffer unordered events in process
 isolation mode

Signed-off-by: Moshe Atlow <moshe@atlow.co.il>
---
 lib/internal/test_runner/runner.js            |  9 +++
 .../execution-ordered-bypass/fast-fail.mjs    |  6 ++
 .../execution-ordered-bypass/slow.mjs         | 12 ++++
 .../test-runner-execution-ordered-bypass.mjs  | 68 +++++++++++++++++++
 4 files changed, 95 insertions(+)
 create mode 100644 test/fixtures/test-runner/execution-ordered-bypass/fast-fail.mjs
 create mode 100644 test/fixtures/test-runner/execution-ordered-bypass/slow.mjs
 create mode 100644 test/parallel/test-runner-execution-ordered-bypass.mjs

diff --git a/lib/internal/test_runner/runner.js b/lib/internal/test_runner/runner.js
index d6cb6438d2b52a..e4f8f6f51d642e 100644
--- a/lib/internal/test_runner/runner.js
+++ b/lib/internal/test_runner/runner.js
@@ -128,6 +128,11 @@ const kDiagnosticsFilterArgs = ['tests', 'suites', 'pass', 'fail', 'cancelled',
 const kCanceledTests = new SafeSet()
   .add(kCancelledByParent).add(kAborted).add(kTestTimeoutFailure);
 
+// Execution-ordered events are forwarded immediately, bypassing the
+// per-file declaration-order buffer.
+const kExecutionOrderedEvents = new SafeSet()
+  .add('test:enqueue').add('test:dequeue').add('test:complete');
+
 let kResistStopPropagation;
 
 // Worker ID pool management for concurrent test execution
@@ -331,6 +336,10 @@ class FileTest extends Test {
     }
   }
   addToReport(item) {
+    if (kExecutionOrderedEvents.has(item.type)) {
+      this.#handleReportItem(item);
+      return;
+    }
     this.#accumulateReportItem(item);
     if (!this.isClearToSend()) {
       ArrayPrototypePush(this.#reportBuffer, item);
diff --git a/test/fixtures/test-runner/execution-ordered-bypass/fast-fail.mjs b/test/fixtures/test-runner/execution-ordered-bypass/fast-fail.mjs
new file mode 100644
index 00000000000000..74b77682b6821d
--- /dev/null
+++ b/test/fixtures/test-runner/execution-ordered-bypass/fast-fail.mjs
@@ -0,0 +1,6 @@
+import { test } from 'node:test';
+import assert from 'node:assert';
+
+test('fast-fail', () => {
+  assert.fail('fast');
+});
diff --git a/test/fixtures/test-runner/execution-ordered-bypass/slow.mjs b/test/fixtures/test-runner/execution-ordered-bypass/slow.mjs
new file mode 100644
index 00000000000000..88e6d7339a492e
--- /dev/null
+++ b/test/fixtures/test-runner/execution-ordered-bypass/slow.mjs
@@ -0,0 +1,12 @@
+import { test } from 'node:test';
+import { setTimeout as sleep } from 'node:timers/promises';
+import { existsSync } from 'node:fs';
+
+test('slow', async () => {
+  const goFile = process.env.NODE_TEST_GO_FILE;
+  for (let i = 0; i < 1200; i++) {
+    if (existsSync(goFile)) return;
+    await sleep(50);
+  }
+  throw new Error('go signal from host never arrived');
+});
diff --git a/test/parallel/test-runner-execution-ordered-bypass.mjs b/test/parallel/test-runner-execution-ordered-bypass.mjs
new file mode 100644
index 00000000000000..f919914c172b4a
--- /dev/null
+++ b/test/parallel/test-runner-execution-ordered-bypass.mjs
@@ -0,0 +1,68 @@
+// Flags: --no-warnings
+
+import '../common/index.mjs';
+import * as fixtures from '../common/fixtures.mjs';
+import tmpdir from '../common/tmpdir.js';
+import assert from 'node:assert';
+import { writeFileSync } from 'node:fs';
+import { test, run } from 'node:test';
+
+const files = [
+  fixtures.path('test-runner', 'execution-ordered-bypass', 'slow.mjs'),
+  fixtures.path('test-runner', 'execution-ordered-bypass', 'fast-fail.mjs'),
+];
+
+test('execution-ordered events bypass FileTest declaration-order buffer', async () => {
+  tmpdir.refresh();
+  const goFile = tmpdir.resolve('execution-ordered-go');
+
+  // Force two-way concurrency. `concurrency: true` would resolve to
+  // `availableParallelism() - 1`, which is 1 on single-core CI runners — and
+  // with one slot the runner spawns the files sequentially, so fast-fail
+  // would never start while slow is polling.
+  const stream = run({
+    files,
+    isolation: 'process',
+    concurrency: 2,
+    env: { ...process.env, NODE_TEST_GO_FILE: goFile },
+  });
+
+  const events = [];
+
+  stream.on('test:complete', (data) => {
+    if (data.name === 'slow' || data.name === 'fast-fail') {
+      events.push(`complete:${data.name}`);
+      if (data.name === 'fast-fail') {
+        writeFileSync(goFile, '');
+      }
+    }
+  });
+
+  stream.on('test:fail', (data) => {
+    if (data.name === 'fast-fail') {
+      events.push(`fail:${data.name}`);
+    }
+  });
+
+  // eslint-disable-next-line no-unused-vars
+  for await (const _ of stream);
+
+  const completeFast = events.indexOf('complete:fast-fail');
+  const completeSlow = events.indexOf('complete:slow');
+  const failFast = events.indexOf('fail:fast-fail');
+
+  assert.notStrictEqual(completeFast, -1);
+  assert.notStrictEqual(completeSlow, -1);
+  assert.notStrictEqual(failFast, -1);
+
+  assert.ok(
+    completeFast < completeSlow,
+    `test:complete for fast-fail should arrive before slow; events=${events.join(', ')}`,
+  );
+
+  // test:fail is declaration-ordered, so the bypass must not affect it.
+  assert.ok(
+    failFast > completeSlow,
+    `test:fail for fast-fail should arrive after test:complete for slow; events=${events.join(', ')}`,
+  );
+});