It is always recommendable to make a zone check before updating name servers in order to be sure that the name servers are correctly configured for your domain.
Depending on the TLD extension, you can use following online zone check tools:
For .FR: Afnic zone check
For .DE: Denic zone check
For .HU: Nic.hu zone check
For .LU: DNS-LU zone check
For .NL: Sidn zone check
Result must be SUCCESS.
NOTE: the zone test tools for .FR and .DE domains are specially thorough and can be also used for other TLD.