I don't think you're asking this question correctly.
Does nto matter how many networks your system is exposed to, your system will only point to one set of root nameservers in /etc/resolv.conf.
Remember that DNS, forwarders, etc.. are just for DNS lookups ONLY, they do not tell your system how to get to the destination but only that the destination for test1.com is 192.168.8.5 and test2.com is 10.10.10.1.
Your routing table tells your system how to get to a destination based upon the IP address.
When you say forwarder I think you are referring to a default gateway that the traffic should be going through.
So can you please confirm that is what you are wanting:
test1.com who has IP address 192.16.8.5 should use
xzy interface and
xyz gateway and test2.com who has IP address 10.10.10.1 should use
abc interface and
abc gateway.
If that is the case, provide the following:
We can then give you the route add statements to add the appropriate routes to the system