```
> require('http').globalAgent.sockets
{ 'HOST:PORT:': [{ ... }, { ... }] }
```
- `new URL('http://HOST:PORT:')` throws
-> test suite `open_sockets`
- gauges were not cleaned up after no agents were present for a given
key. This lead to continuous emission of the previous connection
count for a given hostname, following the completion of all requests.
-> test suite `when all requests complete`
