def METHOD_NAME(self, ispan, ospan):
    """Function passed to `CallbackBlock`, which
        checks data before scrunch"""
    self.assertLessEqual(ispan.nframe, self.gulp_nframe)
    self.assertEqual(ospan.nframe, ispan.nframe)
    self.assertEqual(ispan.data.shape, (ispan.nframe,1,2))
    self.assertEqual(ospan.data.shape, (ospan.nframe,1,2))