Linear acceleration and head-on collisions between electrons and positrons are among the most promising techniques to study physics beyond the Standard Model in the TeV energy range for the post LHC era. For this purpose, it is essential to achieve very high accelerating gradients in order to limit the length of the new machine. The Compact LInear Collider (CLIC) project at CERN is aiming at a gradient of 150 MV/m, thanks to the so-called two-beam acceleration technique: the RF power is extracted from a low-energy and high-intensity drive-beam running parallel to the main beam. In the framework of the RF power source studies, a new CLIC Test Facility (CTF3) is under construction at CERN, in order to demonstrate the feasibility of the electron pulse compression and of the bunch frequency multiplication, which are necessary to produce a drive-beam with a frequency of 30 GHz. An overview of the CTF3 project will be given and the first measurements performed on CTF3 will be presented.