for more of a tester you might try a youngish dog that needs a bit of bringing on or a deeper dig to find out there internal make up to make more time leave it there slightly longer, thats testing a terrier not putting a big dog in a small spot and expecting it to fail, you may challange a terrier with a deep rangy place if its got used to small easier spots but not give it a huge place and again expect it to fail, dogs need bringing on just like we are all brought on in the digging game