From bf846f98845f5519d1eb246bd10a277541d61b1b Mon Sep 17 00:00:00 2001
From: Yarchik <spoko.dev@gmail.com>
Date: Wed, 21 Oct 2026 13:15:37 +0200
Subject: [PATCH] test_runner: run the longest timer in runAll()

PriorityQueue#peekBottom() returned the last slot of the heap, which is
not necessarily the largest element, so MockTimers#runAll() could stop
before the timer that fires last. Scan the leaves of the heap for the
largest element instead.

Assisted-by: a closed-source coding agent
Signed-off-by: Yarchik <spoko.dev@gmail.com>
---
 lib/internal/priority_queue.js           | 10 +++++++++-
 test/parallel/test-runner-mock-timers.js | 13 +++++++++++++
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/lib/internal/priority_queue.js b/lib/internal/priority_queue.js
index e6fdb61e9997..717af91eefdf 100644
--- a/lib/internal/priority_queue.js
+++ b/lib/internal/priority_queue.js
@@ -32,7 +32,15 @@ module.exports = class PriorityQueue {
   }
 
   peekBottom() {
-    return this.#heap[this.#size];
+    const compare = this.#compare;
+    const heap = this.#heap;
+    const size = this.#size;
+    let bottom = heap[size];
+    for (let pos = (size >> 1) + 1; pos < size; pos++) {
+      if (compare(heap[pos], bottom) > 0)
+        bottom = heap[pos];
+    }
+    return bottom;
   }
 
   percolateDown(pos) {
diff --git a/test/parallel/test-runner-mock-timers.js b/test/parallel/test-runner-mock-timers.js
index 25510fe023d0..ba1841b4c91e 100644
--- a/test/parallel/test-runner-mock-timers.js
+++ b/test/parallel/test-runner-mock-timers.js
@@ -195,6 +195,19 @@ describe('Mock Timers Test Suite', () => {
         assert.strictEqual(Date.now(), 9999);
       });
 
+      it('should trigger all timers when the longest one is scheduled first', (t) => {
+        t.mock.timers.enable({ apis: ['setTimeout', 'Date'] });
+        const results = [];
+
+        globalThis.setTimeout(() => results.push(1), 9999);
+        globalThis.setTimeout(() => results.push(3), 8888);
+        globalThis.setTimeout(() => results.push(2), 8888);
+        t.mock.timers.runAll();
+
+        assert.deepStrictEqual(results, [3, 2, 1]);
+        assert.strictEqual(Date.now(), 9999);
+      });
+
       it('should not error if there are not timers to run', (t) => {
         t.mock.timers.enable();
         t.mock.timers.runAll();