Oracles Are Hardly Attain'd, and Hardly Understood: Confessions of Software Testing Researchers

In software testing, a test oracle refers to the mechanism for determining whether the results of the software under test agree with the expected outcomes. To achieve this, we need a means to determine the expected outcomes, a means to gauge the actual results, and a means to decide whether the actual results agree with the expected outcomes. In real-life situations, however, a test oracle may not exist owing to a missing link in any of these aspects. In this paper, we summarize our research for the last 15 years on selected issues related to each of these aspects. We present the use of metamorphic testing, pattern classification, and formal object equivalence and nonequivalence to alleviate the problems.