Hi @kgaurav, and welcome to the LE community forum 
LE doesn't provide certs for IPs [not yet at least - there is talk about them doing that one day].
The CAB forum rules won't allow any trusted CA to issue a cert for names outside of the global DNS.
Names like: "localhost", "*.local", "*.internal" are not allowed.
You should issue your own [self-signed] cert(s) and have the test environment trust them explicitly.