Anyway to confirm whether an evap canister has gone bad?

2014 Kia Forte LX 1.8L Engine 101066 Miles
No DTC codes
Long term fuel trim spikes -12% when putting in park and idling after driving for any length of time that brings the engine up to operating temp.  It eventually settles to around negative 9% after a few minutes of idling.
I suspect an issue with the EVAP canister or the evap purge solenoid (issue could also potentially be in the evap hoses) as this vehicle was over-fueled in the past.  The over fueling issue has been corrected for many fueling cycles (close to a year without over fueling) but I think that the charcoal in the canister could have been compromised.
I am wondering if there is a way to confirm these components are bad through any test methods.  The purge solenoid does cycle between periods of activity and inactivity as I can feel it clicking rapidly at times and then not clicking other times.  When the solenoid is disconnected no major changes occur to the fuel trim numbers.  Perhaps this is an indication that the solenoid is sticking open when its not active and is allowing unwanted vapors to enter the engine?
Anyway if anyone has any suggestions of tests that I could do on the evap system please let me know.
One other thing I forgot to mention.  About a year ago the vehicle had a small evap system leak code with a checking engine light.  I changed the gas cap which didn't correct the issue.  I put a smoke machine on and couldn't see any leaks.  I removed the canister and found a small crack (could barely see it) in the plastic body.  I sealed the crack with some plastic JB Weld compound and the code and check engine light went away.  Haven't had any other leaks since then.  Thanks in advance for any help.

At the Purge Valve, disconnect the EVAP line that runs back to the canister. Leave the intake vacuum line connected. Disconnect the Purge Valve electrical connector. 

With the engine running, put your finger over the disconnected EVAP port of the Purge Valve. Can you feel any vacuum? If you can, replace the Purge Valve. 
If not, reconnect the EVAP line and electrical connector. Using a scan tool, command the Purge Valve on. While watching your fuel trims, disconnect the Canister and watch for a significant change. 

I disconnected the hose at the purge valve and the electrical connector. No vacuum felt with engine running. I left the hose disconnected and plugged the connector back in and heard a pulsing popping noise and felt intermittent vacuum that was in time with those pulsations. I assume that is the normal function of the purge valve. One last question when I use the scan tool to command the purge valve should I disconnect the canister in the same location (at the purge valve) or should I disconnect it at the canister itself in the rear of the vehilce?

I would disconnect it at the canister. That would, possibly, give you the opportunity to see/smell whether or not the canister is flooded.