test_runner: fix run() isolation=none hang in cluster workers

lib/internal/test_runner/runner.js

@@ -942,8 +942,19 @@ function run(options = kEmptyObject) {
         debug('beginning test execution');
         root.entryFile = null;
         finishBootstrap();
-        return root.processPendingSubtests();
+        const pendingSubtestsPromise = root.processPendingSubtests();
+        if (!isTestRunner) {
+          PromisePrototypeThen(pendingSubtestsPromise, undefined, triggerUncaughtException);
+          return;
+        }
+        return pendingSubtestsPromise;
       };
+
+      if (!isTestRunner) {
+        // run() API consumers can keep handles alive (e.g., IPC). Finalize
+        // without waiting for beforeExit so the stream can close promptly.
+        teardown = () => root.harness.teardown();
+      }
     }
   }
 

test/fixtures/test-runner/run-isolation-none-in-cluster.js

@@ -0,0 +1,45 @@
+'use strict';
+
+const cluster = require('node:cluster');
+const { join } = require('node:path');
+const { run } = require('node:test');
+
+if (cluster.isPrimary) {
+  const worker = cluster.fork();
+  worker.on('exit', (code, signal) => {
+    if (signal !== null) {
+      process.stderr.write(`worker exited with signal ${signal}\n`);
+      process.exit(1);
+    }
+
+    process.exit(code ?? 0);
+  });
+} else {
+  // Repro based on: https://github.com/nodejs/node/issues/60020
+  // We pin `files` for deterministic test discovery in CI.
+  const stream = run({
+    isolation: 'none',
+    files: [
+      join(__dirname, 'default-behavior', 'test', 'random.cjs'),
+    ],
+  });
+
+  stream.on('error', (err) => {
+    process.stderr.write(`worker error: ${err}\n`);
+    process.exit(1);
+  });
+
+  stream.on('data', (data) => {
+    process.stdout.write(`on data ${data.type}\n`);
+  });
+
+  stream.on('end', () => {
+    process.stdout.write('on end\n');
+    process.exit(0);
+  });
+
+  setTimeout(() => {
+    process.stderr.write('worker timed out waiting for end\n');
+    process.exit(1);
+  }, 3000).unref();
+}

test/parallel/test-runner-run.mjs

@@ -1,6 +1,7 @@
 import * as common from '../common/index.mjs';
 import * as fixtures from '../common/fixtures.mjs';
 import { join } from 'node:path';
+import { spawnSync } from 'node:child_process';
 import { describe, it, run } from 'node:test';
 import { dot, spec, tap } from 'node:test/reporters';
 import consumers from 'node:stream/consumers';
@@ -646,6 +647,19 @@ describe('require(\'node:test\').run', { concurrency: true }, () => {
       assert.strictEqual(diagnostics.includes(entry), true);
     }
   });
+
+  // Regression test for https://github.com/nodejs/node/issues/60020
+  it('should not hang in cluster workers when isolation is none', () => {
+    const fixture = fixtures.path('test-runner', 'run-isolation-none-in-cluster.js');
+    const { status, signal, stdout, stderr } = spawnSync(process.execPath, [fixture], {
+      encoding: 'utf8',
+      timeout: common.platformTimeout(15_000),
+    });
+
+    assert.strictEqual(signal, null);
+    assert.strictEqual(status, 0, stderr);
+    assert.match(stdout, /on end/);
+  });
 });
 
 describe('env', () => {