Automatic Metamorphic Test Oracles for Action-Policy Testing

Testing is a promising way to gain trust in learned action policies π. Prior work on action-policy testing in AI planning formalized bugs as states t where π is sub-optimal with respect to a given testing objective. Deciding whether or not t is a bug is as hard as (optimal) planning itself. How can we design test oracles able to recognize some states t to be bugs efficiently? Recent work introduced metamorphic oracles which compare policy behavior on state pairs (s,t) where t is easier to solve; if π performs worse on t than on s, we know that t is a bug. Here, we show how to automatically design such oracles in classical planning, based on simulation relations between states. We introduce two oracle families of this kind: first, morphing query states t to obtain suitable s; second, maintaining and comparing upper bounds on h* across the states encountered during testing. Our experiments on ASNet policies show that these oracles can find bugs much more quickly than the existing alternatives, which are search-based; and that the combination of our oracles with search-based ones almost consistently dominates all other oracles.