From the Roland Garros website:
The fight against drugsAbout 200 tests covering how many players across how many draws?
Drug-testing is carried out under the auspices of the International Tennis Federation (ITF).
At the 2013 French Open, almost 200 tests were carried out on players entered in the men's and women's singles and doubles main draws as well as the qualifiers and the juniors' tournaments.
Special areas dedicated to testing are located in the players' zone near to the locker-rooms.