  As quantum computing is becoming increasingly popular, the underlying quantum
computing platforms are growing both in ability and complexity. Unfortunately,
testing these 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) a 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 8k program pairs within
two days, many of which expose crashes. Inspecting the crashes, we find 13
bugs, nine 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.
