MUSE (Multi Unit Spectroscopic Explorer) is a second generation instrument developed for ESO (European Southern Observatory) and will be assembled to the VLT (Very Large Telescope) in 2013. The MUSE instrument can simultaneously record 90.000 spectra in the visible wavelength range (465-930nm), across a 1*1arcmin² field of view, thanks to 24 identical Integral Field Units (IFU). A collaboration of 7 institutes has partly validated and sent their subsystems to CRAL (Centre de Recherche Astrophysique de Lyon) in 2011, where they have been assembled together. The global test and validation process is currently going on to reach the Preliminary Acceptance in Europe in 2012. The sharing of performances has been based on 5 main functional sub-systems. The Fore Optics sub-system derotates and anamorphoses the VLT Nasmyth focal plane image, the Splitting and Relay Optics associated with the Main Structure are feeding each IFU with 1/24th of the field of view. Each IFU is composed of a 3D function insured by an image slicer system and a spectrograph, and a detection function by a 4k*4k CCD cooled down to 163°K. The 5th function is the calibration and data reduction of the instrument. This article depicts the sequence of tests that has been completely reshafled mainly due to planning constraints. It highlights the priority given to the most critical performances tests of the sub-systems and their results. It enhances then the importance given to global tests. Finally, it makes a status on the verification matrix and the validation of the instrument and gives a critical view on the risks taken.
