Current bitcoin-master on testnet, `maxconnections=8` in the config file. Running in VM that doesn't have public IP and is not reachable from the Internet.

Wait until you have 8 peers.

```
telnet localhost 18333
```

It will result in:

```
Assertion failed: (nMaxInbound > 0), function AcceptConnection, file net.cpp, line 973.
```

First found in https://github.com/bitcoin/bitcoin/pull/8996, but can be reproduced on master.

CService service(LookupNumeric(strAddNode.c_str(), Params().GetDefaultPort()));
        if (service.IsValid()) {
            
            auto it = mapConnected.find(service);
            if (it != mapConnected.end()) {
                ret.push_back(AddedNodeInfo{strAddNode, service, true, it->second});
            } else {
                ret.push_back(AddedNodeInfo{strAddNode, CService(), false, false});
            }
        } else {
            
            auto it = mapConnectedByName.find(strAddNode);
            if (it != mapConnectedByName.end()) {
                ret.push_back(AddedNodeInfo{strAddNode, it->second.second, true, it->second.first});
            } else {
                ret.push_back(AddedNodeInfo{strAddNode, CService(), false, false});
            }
        }
    }
    return ret;
}
void CConnman::ThreadOpenAddedConnections()