Test idea: Connectivity test via extendcircuit
Set up a tiny Tor relay somewhere, or otherwise have one that we know is reliably working.
Run a Tor client, and use a controller script to run "extendcircuit 0 x,y" where y is the fixed end server, and x is each relay in the network one at a time.
Write down the "circ" events that come out of it.
We will discover which relays can reach our relay, which lets us infer things like (a) which relays are firewalling outbound connections or outbound ports and (b) which relays are running out of file descriptors.
For best results, we'd want to use an end relay that nobody already has a connection to (since otherwise the circuit creation will reuse the existing connection, and not properly test current connectivity.) The simple hack is to make the end relay tiny and new, so most people won't have open connections to it. (The more elegant way, in the past, would have been to "+postdescriptor" the end relay's descriptor to our local Tor client, and then extendcircuit will be able to use it -- but my guess is that we broke this functionality sometime in the past years.)