async def test_chain_true_during_binary(self):
        """client starts on main chain. client already knows about another fork, which has local height 10.
        server is on that fork but has more blocks.
        - first missing block found during *binary* phase
        - is *existing* fork
        """
        ifa = self.interface
        ifa.tip = 20
        ifa.blockchain = MockBlockchain(["00a", "01a", "02a", "03a", "04a", "05a", "06a", "07a", "08a", "09a", "10a", "11a", "12a", "13a", "14a"])
        blockchain.blockchains = {
            "00a": ifa.blockchain,
            "07b": MockBlockchain(["00a", "01a", "02a", "03a", "04a", "05a", "06a", "07b", "08b", "09b", "10b"]),
        }
        ifa.q.put_nowait({'block_height': 20, 'mock': {CRM.CATCHUP:1, 'id': '20b', 'prev_id': '19b'}})
        ifa.q.put_nowait({'block_height': 15, 'mock': {CRM.BACKWARD:1, 'id': '15b', 'prev_id': '14b'}})
        ifa.q.put_nowait({'block_height': 13, 'mock': {CRM.BACKWARD:1, 'id': '13b', 'prev_id': '12b'}})
        ifa.q.put_nowait({'block_height': 9, 'mock': {CRM.BACKWARD:1, 'id': '09b', 'prev_id': '08b'}})
        ifa.q.put_nowait({'block_height': 11, 'mock': {CRM.BINARY:1, 'id': '11b', 'prev_id': '10b'}})
        ifa.q.put_nowait({'block_height': 10, 'mock': {CRM.BINARY:1, 'id': '10b', 'prev_id': '09b'}})
        ifa.q.put_nowait({'block_height': 11, 'mock': {CRM.CATCHUP:1, 'id': '11b', 'prev_id': '10b'}})
        ifa.q.put_nowait({'block_height': 12, 'mock': {CRM.CATCHUP:1, 'id': '12b', 'prev_id': '11b'}})
        ifa.q.put_nowait({'block_height': 13, 'mock': {CRM.CATCHUP:1, 'id': '13b', 'prev_id': '12b'}})
        res = await ifa.sync_until(ifa.tip, next_height=13)
        self.assertEqual((CRM.CATCHUP, 14), res)
        self.assertEqual(ifa.q.qsize(), 0)
        self.assertEqual(len(blockchain.blockchains), 2)
client starts on main chain. client already knows about another fork, which has local height 10.
        server is on that fork but has more blocks.
        - first missing block found during *binary* phase
        - is *existing* fork
        
tests/test_network.py