test: add regression test for 51586

Signed-off-by: Matteo Collina <hello@matteocollina.com>
PR-URL: #51491
Reviewed-By: Vinícius Lourenço Claro Cardoso <contact@viniciusl.com.br>
Reviewed-By: Marco Ippolito <marcoippolito54@gmail.com>
Reviewed-By: Matthew Aitken <maitken033380023@gmail.com>
Reviewed-By: Rafael Gonzaga <rafael.nunu@hotmail.com>
Reviewed-By: Moshe Atlow <moshe@atlow.co.il>
Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>

test/parallel/test-webstream-structured-clone-no-leftovers.mjs

@@ -0,0 +1,28 @@
+import '../common/index.mjs';
+import { test } from 'node:test';
+import assert from 'node:assert';
+
+test('do not leak promises', async () => {
+  const buf = new Uint8Array(1);
+  const readable = new ReadableStream({
+    start(controller) {
+      controller.enqueue(buf);
+      controller.close();
+    }
+  });
+
+  const [out1, out2] = readable.tee();
+  const cloned = structuredClone(out2, { transfer: [out2] });
+
+  for await (const chunk of cloned) {
+    assert.deepStrictEqual(chunk, buf);
+  }
+
+  for await (const chunk of out2) {
+    assert.deepStrictEqual(chunk, buf);
+  }
+
+  for await (const chunk of out1) {
+    assert.deepStrictEqual(chunk, buf);
+  }
+});