If the nameservers are indicated at the time of registration, the registrar must ensure that at least two nameservers are listed.
All of the nameservers administered by the registrar must be correctly configured and respond authoritatively to DNS queries concerning the zone. The registrar must check and test their own nameservers if these have been indicated and ensure that they respond correctly for the domain requested.
The nameserver test must be conducted prior to the registration being submitted to Registry Services. This type of test can be conducted with the following tool Zonemaster (The registrar can of course use another tool to verify that the servers are responding correctly.)