This should fail now html imports are depreciated.
There's an incorrect http:// canonical to test detection, along with a non-secure image
HTML imports Supported? No
HTML Imports Rendered? It fails
Testing if Googlebot can render html imports:
<link rel="import" href="import-test.html">
<script>
if('import' in document.createElement('link')) {
document.getElementById("supported").innerText = 'Yes';
}
const htmlImport = document.querySelector('link[rel="import"]');
const htmlDoc = htmlImport.import;
const htmlMessage = htmlDoc.querySelector('.red');
const current = document.getElementById("fail");
document.getElementById("result").replaceChild(htmlMessage.cloneNode(true), current);
</script>