The proposal of using Macroscopic Quantum Coherence in a SQUID as a test of the validity of Quantum Mechanics (QM) for macroscopic systems (Leggett A., 1980; Leggett A. and Garg A. 1985) is considered. We note that if only Macroscopic Realism (MR) is assumed but the requirement that the flux measurement is non invasive (NIM) is dropped, only the measurement of the charge would discriminate between QM and MR. This discrimination however depends critically on the experimental parameters. There is a threshold above which QM is consistent with MR but the measurement is invasive as in QM.