Badssl is good to see how clients react to a badly configured certificate, which is a different thing from checking whether your certificate or web site are badly configured.

Also had to find another source for revoked test certificates for the homepage examples and found them here: https://www.ssl.com/sample-valid-revoked-and-expired-ssl-tls.... The badssl ones are expired too which means they are no longer revoked since revocation only lasts the lifetime of the certificates, which makes sense of course.

Its founder, Ivan Ristić, has nice books as well.