Coverage Types for Resource-Based Policies

Coverage Types provide a suitable type mechanism that integrates under-approximation logic to support Property-Based Testing. They are used to type the return value of a function that represents an input test generator. This allows us to statically assert that an input test generator not only produces valid input tests but also generates all possible ones, ensuring completeness. In this paper, we extend the coverage framework to guarantee the correctness of Property-Based Testing with respect to resource usage in the input test generator. This is achieved by incorporating into Coverage Types a notion of effect, which represents an over-approximation of operations on relevant resources. Programmers can define resource usage policies through logical annotations, which are then verified against the effect associated with the Coverage Type.