Integration with TeamCity from JetBrains

We just started using TeamCity for our software build process and already use TestComplete for automation. By reading the thread, I can see that it is possible to integrate the two which is great and I saw the attachments on how. I have a relatively easy question. We own a single build agent license for TeamCity, does anyone know if I have to buy additional licenses to run automation tests? I read the attachments to the thread but I am confused as to whether the automation environments count as agents or not. Note: This may be a better question for a TeamCity forum, but figured I would ask here just in case.