1 files changed, 21 insertions, 0 deletions
diff --git a/testing/web-platform/tests/portals/resources/portal-post-message-during-activate-window.html b/testing/web-platform/tests/portals/resources/portal-post-message-during-activate-window.html
new file mode 100644
index 0000000000..6e220277d9
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/portal-post-message-during-activate-window.html
@@ -0,0 +1,21 @@
+<!DOCTYPE html>
+<body>
+  <script>
+    var portal = document.createElement("portal");
+    portal.src = "simple-portal.html";
+    document.body.appendChild(portal);
+
+    portal.onload = () => {
+      portal.activate();
+      error = "";
+      try {
+        portal.postMessage("message");
+      } catch (err) {
+        error = err.name;
+      }
+      bc = new BroadcastChannel("portals-post-message-during-activate");
+      bc.postMessage(error);
+      bc.close();
+    }
+  </script>
+</body>