async def test_catchup_one_block_behind(self):
        """Single chain, but client is behind. The client's height is 5, server is on block 6.
        - first missing block found during *catchup* phase
        """
        ifa = self.interface
        ifa.tip = 6
        ifa.blockchain = MockBlockchain(["00a", "01a", "02a", "03a", "04a", "05a"])
        blockchain.blockchains = {
            "00a": ifa.blockchain,
        }
        ifa.q.put_nowait({'block_height': 6, 'mock': {CRM.CATCHUP:1, 'id': '06a', 'prev_id': '05a'}})
        res = await ifa.sync_until(ifa.tip)
        self.assertEqual((CRM.CATCHUP, 7), res)
        self.assertEqual(ifa.q.qsize(), 0)
        self.assertEqual(len(blockchain.blockchains), 1)
Single chain, but client is behind. The client's height is 5, server is on block 6.
        - first missing block found during *catchup* phase
        
tests/test_network.py