MorphQ: Metamorphic Testing of Quantum Computing Platforms

As quantum computing is becoming increasingly popular, the underlying quantum computing platforms are growing both in ability and complexity. This growth may cause bugs in the platforms, which hinders the adoption of quantum computing. Unfortunately, testing quantum computing platforms is challenging due to the relatively small number of existing quantum programs and because of the oracle problem, i.e., a lack of specifications of the expected behavior of programs. This paper presents MorphQ, the first metamorphic testing approach for quantum computing platforms. Our two key contributions are (i) a program generator that creates a large and diverse set of valid (i.e., non-crashing) quantum programs, and (ii) set of program transformations that exploit quantum-specific metamorphic relationships to alleviate the oracle problem. Evaluating the approach by testing the popular Qiskit platform shows that the approach creates over 50k program pairs within two days, many of which expose crashes. Inspecting the crashes, we find twelve bugs, eight of which have already been confirmed. MorphQ widens the slim portfolio of testing techniques of quantum computing platforms, helping to create a reliable software stack for this increasingly important field.