"Current" servos use PWM for control. (Most build in last 20-30+ years. Older ones are total analog units.)
The 555 chip can be used for PWM and if looked at bottom of your "Servo Tester," likely find that. If can't read a number for whatever reason, like maker scrape the numbers off, other parts & wiring will show.
Some "Switch Motors" are the same with 555 and servos in 1 box. (And High Cost to buy them.)
Many ways to mount the servos beyond under the table. Some I've seen are hidden in buildings, scenery, and more On the table. Servo Doesn't need to be near the track or use strait wire between them but that's easier.