Its typically a test done at build to ensure the system joints are glued together properly.
There is no situation in your house short of a flood where you will ever fill the pipes or place that stress on them.
If the drains are blocked then its a problem, if stuff flows through the pipe then the pipe is working.
The true inspection would ensure you actually have flow from your house to the sewer line with no restrictions.
A 4 inch line will accept about 715 gallons per minute of flowing fluids...fluids will follow the path of least resistance, hence an open pipe will carry your fluids.
I have had this test performed on my house a few times and the only time it passes is right after the repair (normally between 4 and 8K) to replace $8 worth of pipe that they have yet to show me more than a hairline crack in the PVC.
A plumber will not accept the test unless there is no loss in about 20 minutes
Julie Nelson - Keller Williams