Extension-Aware Automated Testing Based on Imperative Predicates

Bounded exhaustive testing (BET) techniques have been shown to be effective for detecting faults in software. BET techniques based on imperative predicates, enumerate all test inputs up to the given bounds such that each test input satisfies the properties encoded by the predicate. The search space is bounded by the user, who specifies the number of objects of each type and the list of values for each field of each type. To optimize the search, existing techniques detect isomorphic instances and record accessed fields during the execution of a predicate. However, these optimizations are extension-unaware, i.e., they do not speed up the search when the predicate is modified, say due to a fix or additional properties. We present a technique, named iGen, that speeds up test generation when imperative predicates are extended. iGen memoizes intermediate results of a test generation and reuses the results in a future search – even when the new search space differs from the old space. We integrated our technique in two BET tools (one for Java and one for Python) and evaluated these implementations with several data structure pairs, including two pairs from the Standard Java Library. Our results show that iGen speeds up test generation by up to 46.59x for the Java tool and up to 49.47x for the Python tool. Additionally, we show that the speedup obtained by iGen increases for larger test instances.