Update packages/runner-shared/src/event-manager.js

Co-authored-by: Zach Bloomquist <[email protected]>

Author: mjhenkes

packages/runner-shared/src/event-manager.js

@@ -321,7 +321,9 @@ export const eventManager = {
 
     // The window.top should not change between test reloads, and we only need to bind the message event once
     // Forward all message events to the current instance of the multi-origin communicator
-    window.top?.addEventListener('message', ({ data, source }) => {
+    if (!window.top) throw new Error('missing window.top in event-manager')
+
+    window.top.addEventListener('message', ({ data, source }) => {
       Cypress.primaryOriginCommunicator.onMessage({ data, source })
     }, false)
   },