A solver-aided language for test input generation

Developing a small but useful set of inputs for tests is challenging. We show that a domain-specific language backed by a constraint solver can help the programmer with this process. The solver can generate a set of test inputs and guarantee that each input is different from other inputs in a way that is useful for testing. This paper presents Iorek: a tool that empowers the programmer with the ability to express to any SMT solver what it means for inputs to be different. The core of Iorek is a rich language for constraining the set of inputs, which includes a novel bounded enumeration mechanism that makes it easy to define and encode a flexible notion of difference over a recursive structure. We demonstrate the flexibility of this mechanism for generating strings. We use Iorek to test real services and find that it is effective at finding bugs. We also build Iorek into a random testing tool and show that it increases coverage.