When trying to run a test on a specific agent, I have been putting the name of the PC (the name displayed in getTesters.php) into the Specific Tester field in the Advanced options of my private instance. Since upgrading to 2.18 (I was on 2.16 previously), this option no longer seems to work.
I tried setting this option in webpagetest.org, but the test will not run on the specified agent.
Is there an option I am missing to get this to work, or is there an issue?
Sorry, I had commented out the code because bots on WPT were filling it in and leaving junk tests in the work directory associated with invalid testers and it accidentally made it into the release.
There are 2 lines commented out in runtest.php that you just need to uncomment (lines 187 and 188 here: Re-enabled the tester affinity option · WPO-Foundation/webpagetest@885f6f2 · GitHub )
No worries 
. I made the change, restarted the service and now I can run jobs on specified PCs.
Thanks!