1<!DOCTYPE html> 2<meta charset="utf-8"> 3<title>Relevant page used as a test helper</title> 4 5<script> 6// incumbent.html will end up posting a message to here. We need to signal back the "source". 7 8window.onmessage = e => { 9 const testId = e.data; 10 const sourceURL = e.source.document.URL; 11 12 window.dispatchEvent(new CustomEvent("messagereceived", { detail: [testId, sourceURL] })); 13}; 14</script> 15