Your Headline

No href: Expect no rel tag
Href local/absolute: Test Href local/absolute Expect no rel tag
Href local/domain: Test Href local/domain Expect no rel tag
Href local/www.domain: Test Href local/www.domain Expect no rel tag
Href external, no target: Test Href external, no target Expect no rel tag
Href external, target not _blank: Test Href external, target not _blank Expect no rel tag
Href external, target _blank: Test Href external, target _blank Expect rel="noopener"
Href external, nofollow exists, target _blank: Test Href external, nofollow exists, target _blank Expect rel="noopener nofollow"

Local link

Offsite link

Offsite link with nofollow

Your first paragraph ...