Maybe testing isn't the right word... I'm assuming they'll be training the crew that will be moving the cars from the siding to blissville on the does and don'ts of shuffling the cars around. I'm assuming they are new hires with no or limited RR experience.
The siding and pretty much all of blissville is new or newly connected track that hasn't seen loaded cars. It looks like they'll be backing up in one direction, over two crossings, so there's safety considerations (both have gates, but I assume someone will walk and flag)
There's also the personnel that'll be moving the containers to and from the loading building, loading the containers on and off the flat cars, etc.
I'd imagine they'll want to make a few dry runs before actual work begins.