Part 2: Add tests for the propagation of focusin and focusout events through a disabled form-associated custom element.

Differential Revision: https://phabricator.services.mozilla.com/D173176

bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1818287
gecko-commit: a4ec639e1547c3d1e670b112dc1fcccbe1f8d0bf
gecko-reviewers: edgar
diff --git a/custom-elements/form-associated/disabled-delegatesFocus.html b/custom-elements/form-associated/disabled-delegatesFocus.html
index f92cc52..3f2b765 100644
--- a/custom-elements/form-associated/disabled-delegatesFocus.html
+++ b/custom-elements/form-associated/disabled-delegatesFocus.html
@@ -36,10 +36,21 @@
 </form>
 
 <script>
+  let focusinPropagated = false;
+  let focusoutPropagated = false;
+
+  const form = document.querySelector("form");
+  form.addEventListener("focusin", () => focusinPropagated = true);
+  form.addEventListener("focusout", () => focusoutPropagated = true);
+
   test(() => {
     const element = document.querySelector("custom-control");
     element.focus();
 
     assert_true(element.eventFired, "Focus event fired on custom control");
+    assert_true(focusinPropagated, "FocusIn event propagated through control");
+
+    element.blur();
+    assert_true(focusoutPropagated, "FocusOut event propagated through control");
   }, "Focus events fire on disabled form-associated custom elements with delegatesFocus");
 </script>