test_runner: extraneous async activity make a failure

Fixes: nodejs#44612

doc/api/test.md

@@ -272,7 +272,7 @@ top level of the file's TAP output.
 
 The second `setImmediate()` creates an `uncaughtException` event.
 `uncaughtException` and `unhandledRejection` events originating from a completed
-test are handled by the `test` module and reported as diagnostic warnings in
+test are marked as failed by the `test` module and reported as diagnostic warnings in
 the top level of the file's TAP output.
 
 ```js

lib/internal/test_runner/harness.js

@@ -46,6 +46,7 @@ function createProcessEventHandler(eventName, rootTest) {
         `triggered an ${eventName} event.`;
 
       rootTest.diagnostic(msg);
+      process.exitCode = 1;
       return;
     }
 

test/fixtures/test-runner/extraneous_set_immediate_async.mjs

@@ -0,0 +1,5 @@
+import test from 'node:test';
+
+test('extraneous async activity test', () => {
+  setImmediate(() => { throw new Error(); });
+});

test/fixtures/test-runner/extraneous_set_timeout_async.mjs

@@ -0,0 +1,5 @@
+import test from 'node:test';
+
+test('extraneous async activity test', () => {
+  setTimeout(() => { throw new Error(); }, 100);
+});

test/parallel/test-runner-extraneous-async-activity.js

@@ -0,0 +1,24 @@
+'use strict';
+const fixtures = require('../common/fixtures');
+const assert = require('assert');
+const { spawnSync } = require('child_process');
+
+{
+  const child = spawnSync(process.execPath, ['--test', fixtures.path('test-runner', 'extraneous_set_immediate_async.mjs')]);
+  const stdout = child.stdout.toString();
+  assert.match(stdout, /^# pass 0$/m);
+  assert.match(stdout, /^# fail 1$/m);
+  assert.match(stdout, /^# cancelled 0$/m);
+  assert.strictEqual(child.status, 1);
+  assert.strictEqual(child.signal, null);
+}
+
+{
+  const child = spawnSync(process.execPath, ['--test', fixtures.path('test-runner', 'extraneous_set_timeout_async.mjs')]);
+  const stdout = child.stdout.toString();
+  assert.match(stdout, /^# pass 0$/m);
+  assert.match(stdout, /^# fail 1$/m);
+  assert.match(stdout, /^# cancelled 0$/m);
+  assert.strictEqual(child.status, 1);
+  assert.strictEqual(child.signal, null);
+}