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.

{
    LOCK(cs_vAddedNodes);
    for(std::vector<std::string>::iterator it = vAddedNodes.begin(); it != vAddedNodes.end(); ++it) {
        if (strNode == *it) {
            vAddedNodes.erase(it);
            return true;
        }
    }
    return false;
}
size_t CConnman::GetNodeCount(NumConnections flags)
{
    LOCK(cs_vNodes);
    if (flags == CConnman::CONNECTIONS_ALL) 
        return vNodes.size();
    int nNum = 0;
    for(std::vector<CNode*>::const_iterator it = vNodes.begin(); it != vNodes.end(); ++it)
        if (flags & ((*it)->fInbound ? CONNECTIONS_IN : CONNECTIONS_OUT))
            nNum++;
    return nNum;
}
void CConnman::GetNodeStats(std::vector<CNodeStats>& vstats)