Testing Is … Freedom To Change
For this second entry in the “Testing Is …” series, I decided to mention an advantage of testing that is widely known. The idea is not original, but its importance to you as a developer cannot be overstated. Perhaps the single greatest advantage of writing tests is the freedom you feel to change the code under test. All software grows cruft over time, and left unchecked the code will become an unmaintainable mess. Most developers would agree that maintaining code is not the greatest part of the job, and maintaining crufty code is about as bad as it gets. The answer is to refactor to remove the cruft over time. However, we also know from bitter experience that changing working code, no matter how crufty, will introduce new bugs1.
That is where the tests come in. If you have maintained a comprehensive test suite over time2, you need not fear nasty new surprises. You can refactor as required, and keep your code base much healthier. Now, test suites are not perfect and new bugs are still bound to happen. However, this is mitigated by two factors:
- The difficulty in maintenance of the crufty code itself will lead to bugs.
- A well-written test suite will cover those dark corners where bugs have been found to lurk. In particular, regression tests written to reproduce bugs as they are found are priceless at refactor time.
The logic is quite simple. Beyond that, there is also a powerful emotional difference. When the tests aren’t in place, we fear change. When we have the testing safety net, the fear is replaced with a sense of freedom. A freedom to change, and improve over time. A freedom which itself can be motivating.
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1 If the cruft has grown due to the underlying complexity of the problem domain it is certain there are some nasty new bugs waiting for you!
2 Maintaining the tests as you write the code is important in itself. It is much more difficult to add tests later, not least because the problem is not fresh in your mind.
