It’s widely noted and accepted that tests result in better code. My conjecture is that tests result in vastly improved programmers.
Even with a good test suite, the first implementation of a project will be utilitarian, complying with the edict of “just get it working!”. This are the red and green phases of the red/green/refactor cycle: red is when the tests fail, and green is when they pass. Too often, that initial version is the end of the cycle for many programmers and projects, which is why, in general, version 1 of a program is horrible:
In the refactoring phase the project goes from simply “working” to being well-crafted. Thus the programmer as well has changed their mindset from writing “working” code to writing well-crafted code, and the programmer has been elevated to a higher level of craftsmanship.
Refactoring code is when a programmer can develop their skills and push the boundaries of their knowledge, such as delving into advanced object-oriented programming and metaprogramming, which are often considered dauntingly complex and risky. But used properly, they can dramatically improve a project, and I believe what is more important, they can dramatically improve the programmer.
In my experience, this was first proven to me when I was working on a large C++ project, my module being our persistence layer, providing a J2EE-like (but vastly simpler) interface with PostgreSQL. Although in that era (the late 1990s) Test-Driven Development hadn’t become popular, my daily goal was to write more test code than “real” code, usually between 500 and 1500 lines per day, usually, but not always, writing my tests first.
As my test suite grew and I became more confident in its ability to catch errors, I pushed my knowledge of C++, particularly with templates and the Standard Template Library, eventually reaching a point when I really understood the magic of the STL code. Had I not had such tests, and thus confidence, I likely would have refrained from pushing myself into an area that previously was in the dark, murky area of C++ to me, and I would not have gained valuable expertise as a C++ programmer.
In fact, I’d say that it’s only because of tests that I’ve felt confident learning a new language, such as when I rewrote DiffJ in JRuby, a language I hadn’t used. Having a thorough test suite made the learning process much easier.
The bottom line is that programmers must understand that testing includes refactoring (including of the test code itself), and that the refactoring phase is where programmers, and projects, can become significantly better.
Oh, and with thorough refactoring that horrible version 1 can eventually lead to significant improvements: