You probably found a lot of online tools to check for DNS Poisoning check. For example, here and here. The second one is a site of Dan Kaminsky - the original researcher that discovered the vulnerability. But, these tools check “My DNS Server” - something that is my ISP server, and not DNS that I am hosting/running. So, after some looking around, a found this one-liner here: just find any Linux box, and type there:

dig @ns1.nameserver.com +short porttest.dns-oarc.net TXT

where ns1.nameserver.com is either IP or name of a DNS server. If the result is GOOD - it’s like that - anything else is a big problem.