From dca8c0e6e495f80f50fe84249a930182411e6e63 Mon Sep 17 00:00:00 2001
From: Jayson Chen <jaysonchen@microsoft.com>
Date: Mon, 24 Nov 2025 14:17:46 -0800
Subject: [PATCH] Add test to verify "keep custom element registry null"
 behavior for shadowroot

---
 .../registries/element-mutation.html            | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/custom-elements/registries/element-mutation.html b/custom-elements/registries/element-mutation.html
index 9ed6fa7d0b2b3f..817965d260a8a3 100644
--- a/custom-elements/registries/element-mutation.html
+++ b/custom-elements/registries/element-mutation.html
@@ -20,6 +20,15 @@
     </div>
 </div>
 
+<template id="template">
+    <div id="template-host-1">
+        <template shadowrootmode="open" shadowrootclonable><x-foo></x-foo></template>
+    </div>
+    <div id="template-host-2">
+        <template shadowrootmode="open" shadowrootclonable shadowrootcustomelementregistry><x-foo></x-foo></template>
+    </div>
+</template>
+
 <script>
 
 test(() => {
@@ -66,5 +75,13 @@
     assert_equals(element.customElementRegistry, registry1);
 }, "An element with scoped registry should not change its registry when moved into another shadow tree with different scoped registry.")
 
+test(() => {
+    customElements.define('x-foo', class extends HTMLElement {});
+    const template = document.getElementById('template');
+    document.body.append(template.content.cloneNode(true));
+    assert_equals(document.querySelector('#template-host-1').shadowRoot.querySelector('x-foo').customElementRegistry, customElements);
+    assert_equals(document.querySelector('#template-host-2').shadowRoot.querySelector('x-foo').customElementRegistry, null);
+}, "Declarative shadow DOM with shadowrootcustomelementregistry attribute without registry initialized should remain null registry after adoption.")
+
 </script>
 </body>