Requirement's Testing - I dont think so there is something like requirement testing. but as a tester I review all the requirements, attend review meetings, if i have any issues with the requirements I will clarify those with team members/team lead, and if not possible with team members/Team lead i will approach with BA for clarifications.
that how I am involved.

but If there are any changes in the requirements or any requirement is added unnecessarily or requirements or not correct etc., for these kind of issues will raise in the issue tracking system. 

Plz correct me if i am wrong