Compile-time Unit Testing

Unit testing is an essential part in high quality software development. The prerequisite of the system-wide test is that all components are working correctly. Such components are checked by unit tests which are focused on small part of code. Unit tests are isolated from other code fragments and are frequently programmed by using third party tools. In this paper we show how to minimalize the number of the required third party tools, and how to automate unit tests. We aimed to express unit tests as part of the source code, and execute them during the compilation to ensure the quality of the code. Two different approaches are presented in this paper: the first is based on the C++11's new mechanisms, such as constant expressions, and static assertions; the second is based on our experimental programming language, Welltype, which offers more flexible unit testing than C++11 – however, both technique are similar. The key in both approaches to get the compiler to execute additional, user defined calculations which can result errors during the compilation. In C++11 the static assertions are used to evaluate parts of the unit tests. Since constant expressions are restricted, in this paper we also present a method how to overcome those restrictions, and how to utilize static assertion with constant expressions. Finally, we describe how our experimental language offers compiler support to evaluate pure expressions at compile-time.