plumbing test on cracked foundation?

We have a cracked foundation. We are wanting to have the foundation repaired, but there have been three sewer blockages in the last two years. I'm worried there may be broken lines. This is a rent house so I don't know the cause of the blockages (they had kids and from babysitting grandkids I know little ones have a love affair with toilet paper). My wife and I are trying to decide whether to run a plumbing test before and after the repair. She says it's a waste of money to do both and I want to know what I'm looking at before I spend the money on the foundation repair. What does a plumbing test cost? Should we do one before and after? Thanks for any help on this.