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.

mapNetGroupNodes[node.nKeyedNetGroup].push_back(node);
        int64_t grouptime = mapNetGroupNodes[node.nKeyedNetGroup][0].nTimeConnected;
        size_t groupsize = mapNetGroupNodes[node.nKeyedNetGroup].size();
        if (groupsize > nMostConnections || (groupsize == nMostConnections && grouptime > nMostConnectionsTime)) {
            nMostConnections = groupsize;
            nMostConnectionsTime = grouptime;
            naMostConnections = node.nKeyedNetGroup;
        }
    }
    
    vEvictionCandidates = std::move(mapNetGroupNodes[naMostConnections]);
    
    NodeId evicted = vEvictionCandidates.front().id;
    LOCK(cs_vNodes);
    for(std::vector<CNode*>::const_iterator it(vNodes.begin()); it != vNodes.end(); ++it) {
        if ((*it)->GetId() == evicted) {
            (*it)->fDisconnect = true;
            return true;
        }
    }
    return false;
}
void CConnman::AcceptConnection(const ListenSocket& hListenSocket) {