Gaia* is Europe's astrometry satellite which is currently entering its operational phase. The Gaia mission will determine the astrometric, photometric properties, as well as the radial velocities of over one billion stellar objects. The observations collected over 24 hours by Gaia will consist of several tens of, up to more than one hundred, million of imagery data files, and low and high resolution spectra. This avalanche of data will be handled by the Gaia Data Processing and Analysis Consortium (DPAC) which is tasked with the processing of the collected data and to ultimately compile the Gaia catalogue. In order to prepare itself for taking up this challenge, DPAC has conducted a number of campaigns simulating its daily operations. Here we will describe these operation rehearsals, their preparation, conduct, and the return of experience. The positive experiences from these campaigns are now being used to also conduct such campaigns for DPAC's long term processing, based on real data.