Checkcertificate details and Expiry of Certificates
You might need to put sudo before above command.
The command will show details of all the certificates on your server, and theirExpiry dates.
Test all configurations/Input before requesting actual certificate
When you try to request a new or renew certificate from LetsEncrypt, and if there is some error in your request. LetsEncrypt might block you for certain time period (1 day or 2 days). It has a finite quota for each domain requests.
So, there is a way to test whether your request is OK or not. It is a great way not to block yourself.