The test chip is something after fabrication of the designed chip it has to be given to the on board testing that whether ur chip is working fine or not that chip is called as test chip..
Or before giving to the onboard testing the chip is called as normal chip
As Far as I understand Normal Chip is something that you design for a particular function. This undergoes testing and then finally goes into production.
On the other hand test chip is used to validate IPs, IO buffersand also get different parameters/values (like delay, resistance) etc for a particular process. Test Chip is just meant for this purpose and does not go into production.