def METHOD_NAME(self):
    """Boltzmann sampling (multiple structures, a.k.a. pbacktrack_cb)"""
    fc = prepare_fc()
    ss = list()
    i = fc.pbacktrack(100, store_structure, ss)
    self.assertEqual(i, 100)
    self.assertEqual(len(ss), 100)
    for s in ss:
        self.assertEqual(len(s), len(sequence))