test: deflake test runner timeout coverage

Use a dedicated fixture with a pending promise and assertion plan
instead of competing assertion timers. Keep both timeout failure
assertions and clear the keepalive interval after the tests finish.

Signed-off-by: Filip Skokan <panva.ip@gmail.com>
Assisted-by: Codex
PR-URL: #66255
Reviewed-By: Aviv Keller <me@aviv.sh>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>

Author: panva

test/fixtures/test-runner/run-timeout.mjs

@@ -0,0 +1,11 @@
+import test, { after } from 'node:test';
+
+// Keep the event loop alive until both tests time out.
+const interval = setInterval(() => {}, 1000);
+after(() => clearInterval(interval));
+
+test('pending promise', () => new Promise(() => {}));
+
+test('pending assertion plan', (t) => {
+  t.plan(1, { wait: true });
+});

test/parallel/test-runner-run.mjs

@@ -90,7 +90,7 @@ describe('require(\'node:test\').run', { concurrency: true }, () => {
 
   it('should support timeout', async () => {
     const stream = run({ timeout: 50, files: [
-      fixtures.path('test-runner', 'plan', 'timeout-basic.mjs'),
+      fixtures.path('test-runner', 'run-timeout.mjs'),
     ] });
     stream.on('test:fail', common.mustCall((data) => {
       assert.strictEqual(data.details.error.failureType, 'testTimeoutFailure');