  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 7 equations which differ essentially from
the $Q_V$ equation introduced by Viallet and thus from the Adler-Bobenko-Suris
list of equations therein contained.
