Design Assertions: Executable Assertions for Design Constraints

An assertion is a Boolean expression embedded in a program that must hold during the execution. Executable assertions are a simple but practical way to check assumptions and code logic at runtime. Assertions are written by referring to concrete program states. In this paper, we recognize a variety of assertions that we call design assertions. These are assertions written to ensure design constraints and properties, not detailed implementation decisions, and thus can detect major problems in the implementation such as design drift or corrosion. However, they are written by referring to concrete program states, thus causing readability and maintenance problems. To address these problems, we propose to write design constraints at a higher abstraction level by referring to abstract program states. We explain our approach using the Dart/Flutter platform, but it should work in other languages and platforms with similar assertion facilities.