This may be more work than you are looking for, but as it's something that we do a lot of in our environment, I thought I'd describe our process..
We have around 6500 toll free numbers that route to us, and we have a need to test each of them every so often to confirm that our upstream carriers haven't done anything stupid. In our case, we also want these test calls to completely skip the normal call routing that would occur for these TFNs, whether that would go to Attendant or to our custom workgroup logic.
The way we do this is by defining a specific "test" ANI that the test calls will come from. Then, inside of the CustomAnswer handler, one of the first things we do is check whether the call is coming from that ANI. If it is, we redirect the call to a handler that saves the result of the test call. In our case, what we actually do is publish an event via a Redis pub/sub instance, which a different process is listening for -- but it would be easy to just use the ODBC steps to write the test call result into a database somewhere instead. We then choose to return busy to the caller instead of even connecting the call, so that we don't incur any toll free charges for the attempt.
As for how we trigger the test call itself, in our case we use a custom application which uses Twilio to place the call -- though you could easily do it via a handler on a timer basis or through an IceLib application. We chose to use Twilio directly to place the call primarily because Twilio is not a part of our carrier infrastructure, and so it made a good test of how our calls route for "everyone else". Depending on the carrier, sometimes if you dial a TFN that is provisioned on that carrier they will short-circuit the SMS/800 lookup and not pay attention to the call routing record. Saves them some money, but for our use case was not a valid test. Hence our use of Twilio to dial.
Not sure if this helps at all -- it wouldn't end up testing whether the call routes to Attendant, but I assume your concern is more carrier level than I3 level anyway.
Cheers,
Joe