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James O Coplien

Unit testing was a staple of the FORTRAN days, when a function was a function and was sometimes worthy of functional testing. Computers computed, and functions and procedures represented units of computation. In those days the dominant design process composed complex external functionality from smaller chunks, which in turn or chestrated yet smaller chunks, and so on down to the level of well-understood primitives.

Each layer supported the layers above it. You actually stood a good chance that you could trace the functionality of the things at the bottom, called functions and procedures, to the requirements that gave rise to them out at the human interface. There was hope that a good designer could understand a given function’s business purpose. And it was possible, at least in well-structured code, to reason about the calling tree. You could mentally simulate code execution in a code review.

Object orientation slowly took the world by storm, and it turned the design world upside-down. First, the design units changed from things-that-computed to small heterogeneous composites called objects that combine several programming artefacts, including functions and data, together inside one wrapper. The object paradigm used classes to wrap several functions together with the specifications of the data global to those functions. The class became a cooki e cutter from which objects were created at run time. In a given computing context, the exact function to be called is determined at run-time and cannot be deduced from the source code as it could in FORTRAN. That made it impossible to reason about run-time behaviour of code by inspection alone. You had to run the program to get the faintest idea of what was going on.

So, testing became in again. And it was unit testing with a vengeance.

Why Most Unit Testing is Waste

Publié le 29 octobre 2016.