Modeling Examples to Test and Understand Software

Abstract

One of the oldest techniques to explain abstract concepts is to provide concrete examples. By explaining an abstract concept with a concrete example people make sure that the concept is understood and remembered. Examples in software can be used both to test the software and to illustrate its functionality. Object-oriented programs are built around the concepts of classes, methods and variables, where methods are the atoms of the functionality. But the meta-models of object-oriented languages do not allow developers to associate runnable and composable examples with these concepts and particularly not with methods. Unit tests on the other hand, assure the quality of the units under test and document them. Not being integrated into the language, unit tests are not linked explicitly to their units under test which makes it unnecessarily dif ficult to use them for documenting, typing and debugging software. In addition they are not composable making it hard to develop higher level test scenarios in parallel with higher level objects. In this thesis we analyze unit tests to learn about implicit dependencies among tests and from tests to the methods under test. We develop a technique to partially order unit tests in terms of their covered methods, which reveals possible redundancies due to the lack of composability. We show how partial orders can be used to debug and to comprehend software. We then develop a taxonomy based on several case studies revealing that a high fraction of unit tests already implicitly focuses on single methods. We show that the rest of the tests can be decomposed into commands focusing on single methods. We build a meta-model based on our findings of analyzing test interdependencies which establishes how tests can be explicitly linked to their method under test and how they can be composed to form higher-level test scenarios. We explain how the problems of missing links between tests and units under test are solved using our meta-model. Furthermore, we implemented the meta-model and a first user interface on top of it to give first evidence of how our model supports the developer.