Grade 3 & 6 testing (EQAO) is a way the Ontario Ministry of Education developed, to measure how well students are doing. They use the results to see if students, parents, teachers and schools can do things better or differently to get better results.
Everyone feels a little stressed at testing times. I'm sure your teacher, principal or another adult in your school would be happy to talk to you about it.
You can go to the EQAO website, to find tips and info on how to prepare.
http://www.eqao.com/