What is it?
This test will check if all links to external pages that have the target="_blank" attribute also have the rel="noopener" or rel="noreferrer" attribute.
When you link to an external site using the target="_blank" attribute, security and performance issues arise:
The other page can access your window object with the window.opener property. This may allow the other page to redirect your page to a malicious URL.
Adding rel="noopener" or rel="noreferrer" to your target="_blank" links avoids these issues.