From 3f8cc88009eff38986964d99180de730898e5753 Mon Sep 17 00:00:00 2001
From: Ben Richeson <benricheson101@gmail.com>
Date: Tue, 2 Apr 2024 15:06:37 -0400
Subject: [PATCH] test_runner: fix clearing final timeout in own callback

PR-URL: https://github.com/nodejs/node/pull/52332
Fixes: https://github.com/nodejs/node/issues/52325
Reviewed-By: Moshe Atlow <moshe@atlow.co.il>
Reviewed-By: Chemi Atlow <chemi@atlow.co.il>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
---
 lib/internal/test_runner/mock/mock_timers.js |  2 +-
 test/parallel/test-runner-mock-timers.js     | 13 +++++++++++++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/lib/internal/test_runner/mock/mock_timers.js b/lib/internal/test_runner/mock/mock_timers.js
index fa4c13a5dec6dc..fdb0935ab64686 100644
--- a/lib/internal/test_runner/mock/mock_timers.js
+++ b/lib/internal/test_runner/mock/mock_timers.js
@@ -652,7 +652,7 @@ class MockTimers {
 
       // Check if the timeout was cleared by calling clearTimeout inside its own callback
       const afterCallback = this.#executionQueue.peek();
-      if (afterCallback.id === timer.id) {
+      if (afterCallback?.id === timer.id) {
         this.#executionQueue.shift();
         timer.priorityQueuePosition = undefined;
       }
diff --git a/test/parallel/test-runner-mock-timers.js b/test/parallel/test-runner-mock-timers.js
index 9af58d5cab0008..6ce6c28c95e326 100644
--- a/test/parallel/test-runner-mock-timers.js
+++ b/test/parallel/test-runner-mock-timers.js
@@ -548,6 +548,19 @@ describe('Mock Timers Test Suite', () => {
           t.mock.timers.runAll();
           assert.strictEqual(f.mock.callCount(), 3);
         });
+
+        it('should allow clearing timeout inside own callback', (t) => {
+          t.mock.timers.enable({ apis: ['setTimeout'] });
+          const f = t.mock.fn();
+
+          const timer = nodeTimers.setTimeout(() => {
+            f();
+            nodeTimers.clearTimeout(timer);
+          }, 50);
+
+          t.mock.timers.runAll();
+          assert.strictEqual(f.mock.callCount(), 1);
+        });
       });
 
       describe('setInterval Suite', () => {