Sewerage Test

A friend of mine was told that he had to get a sewerage test on a house he was planning to buy. He was told that it was going to cost 3 grand to get done. I know about the camera and video to see if there are any roots that have cracked and found its way into the piping system going to the street main sewer causing a leak and I have also heard but never seen the smoke test done in the house but what does a sewerage test consists of ?? The house has a public waste system Thanks Rick