Generalized symmetry integrability test for discrete equations on the square lattice

We present an integrability test for discrete equations on the square lattice, which is based on the existence of a generalized symmetry. We apply this test to a number of equations obtained in different recent papers. As a result we prove the integrability of seven equations which differ essentially from the QV equation introduced by Viallet and thus from the Adler-Bobenko-Suris list of equations contained therein