From 7b19708dec3249df891ad0b5edff43c5d4009043 Mon Sep 17 00:00:00 2001
From: hotpineapple <brandnew.cheese@gmail.com>
Date: Fri, 15 Aug 2025 15:11:50 +0900
Subject: [PATCH] test_runner: set mock timer's interval undefined

prevent adding timer to execution queue if clearInterval() called
---
 lib/internal/test_runner/mock/mock_timers.js |  1 +
 test/parallel/test-runner-mock-timers.js     | 21 ++++++++++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/lib/internal/test_runner/mock/mock_timers.js b/lib/internal/test_runner/mock/mock_timers.js
index f955bea8089deb..490f8cd06fc549 100644
--- a/lib/internal/test_runner/mock/mock_timers.js
+++ b/lib/internal/test_runner/mock/mock_timers.js
@@ -321,6 +321,7 @@ class MockTimers {
     if (timer?.priorityQueuePosition !== undefined) {
       this.#executionQueue.removeAt(timer.priorityQueuePosition);
       timer.priorityQueuePosition = undefined;
+      timer.interval = undefined;
     }
   }
 
diff --git a/test/parallel/test-runner-mock-timers.js b/test/parallel/test-runner-mock-timers.js
index 722c2b362d61e1..f99936f449bc77 100644
--- a/test/parallel/test-runner-mock-timers.js
+++ b/test/parallel/test-runner-mock-timers.js
@@ -201,6 +201,27 @@ describe('Mock Timers Test Suite', () => {
         // Should not throw
       });
     });
+
+    it('interval cleared inside callback should only fire once', (t) => {
+      t.mock.timers.enable();
+      const calls = [];
+
+      setInterval(() => {
+        calls.push('foo');
+      }, 10);
+      const timerId = setInterval(() => {
+        calls.push('bar');
+        clearInterval(timerId);
+      }, 10);
+
+      t.mock.timers.tick(10);
+      t.mock.timers.tick(10);
+
+      assert.deepStrictEqual(
+        calls,
+        ['foo', 'bar', 'foo'],
+      );
+    });
   });
 
   describe('globals/timers', () => {