A Language-Recognition Approach to Unit Testing Message-Passing Systems

Abstract: This thesis addresses the problem of unit testing components in message-passing systems. A message-passing system is one that comprises components communicating with each other solely via the exchange of messages. Testing aids developers in detecting and fixing potential errors and with unit testing in particular, the focus is on independently verifying the correctness of single components, such as functions and methods, in a system whose behavior is well understood. With the aid of unit testing frameworks such as those of the xUnit family, this process can not only be automated and done iteratively, but easily interleaved with the development process, facilitating rapid feedback and early detection of errors in the system. However, such frameworks work in an imperative manner and as such, are unsuitable for verifying message-passing systems where the behavior of a component is encoded in its stream of exchanged messages. In this work, we recognise that similar to streams of symbols in the field of formal languages and abstract machines, one can specify properties of a component’s message stream such that they form a language. Unit testing a component thus becomes the description of an automaton that recognizes such a specified language. We propose a platform-independent, language-recognition approach to creating unit testing frameworks for describing and verifying the behavior of message-passing components, and use this approach in creating a prototype implementation for the Kompics component model. We show that this approach can be used to perform both black box and white box testing of components, and that it is easy to work with while preventing common mistakes in practice.