badssl.com offers a lot of links to subdomains with different tls configurations. This is helful to test how clients behave in certain situations.

Here some examples.

user@laptop:~$ curl https://self-signed.badssl.com/
curl: (60) SSL certificate problem: self-signed certificate
More details here: https://curl.se/docs/sslcerts.html

curl failed to verify the legitimacy of the server and therefore could not
establish a secure connection to it. To learn more about this situation and
how to fix it, please visit the web page mentioned above.

user@laptop:~$ curl https://expired.badssl.com/
curl: (60) SSL certificate problem: certificate has expired
More details here: https://curl.se/docs/sslcerts.html

curl failed to verify the legitimacy of the server and therefore could not
establish a secure connection to it. To learn more about this situation and
how to fix it, please visit the web page mentioned above.

user@laptop:~$ curl https://dh480.badssl.com/
curl: (35) error:0280007E:Diffie-Hellman routines::modulus too small