Automatic Extraction of Object-Oriented Observer Abstractions from Unit-Test Executions

Unit testing has become a common step in software development. Although manually created unit tests are valuable, they are often insufficient; therefore, programmers can use an automatic unit-test-generation tool to produce a large number of additional tests for a class. However, without a priori specifications, programmers cannot practically inspect the execution of each automatically generated test. In this paper, we develop the observer abstraction approach for automatically extracting object-state-transition information of a class from unit-test executions, without requiring a priori specifications. Given a class and a set of its initial tests generated by a third-party tool, we generate new tests to augment the initial tests and produce the abstract state of an object based on the return values of a set of observers (public methods with non-void returns) invoked on the object. From the executions of both the new and initial tests, we automatically extract observer abstractions, each of which is an object state machine (OSM): a state in the OSM represents an abstract state and a transition in the OSM represents method calls. We have implemented the Obstra tool for the approach and have applied the approach on complex data structures; our experiences suggest that this approach provides useful object-state-transition information for programmers to inspect unit-test executions effectively.