Unit testing is really really boring. It is waste of time and productivity, writing unit-tests is hard, takes long and might require time-taking refactorings to the code for it to be unit-testable. Regression testing is anyway a lot more effective in finding mistakes. Besides, unit testing provides very little value as it doesn’t tell anything about the quality of the software. Adding unit tests to code which has already been proven working by functional testing is just stupid.
That may sound a bit exaggerated, but I’m almost serious here. There are times when adding unit tests is really waste of time. There’s a lot of code which is hard or near impossible to unit test properly. But the last part about code being proven working by functional testing is in my opinion bullshit. Functional testing tests functionality and can prove that desired functionality has been achieved, but it cannot prove that the code does what the developer intended it to do. And no matter how much functional tests you add on top of your software, it doesn’t make the code any more maintainable.
Let me tell you how I define testing and unit testing.
Testing gives quality information about software. Qualities being e.g. functionality, usability, reliability, performance etc. We do testing in order to determine the current quality level of a certain software. This information can be further used to make decisions e.g. whether to release the software now or later (or never which is a brilliant decision in some cases).
Unit testing does not give you any quality information about the software or it’s functionality, but it does give you information about the quality the code. There is a difference. Unit testing, if done properly, can prove that the code does exactly what the developer intended it to do. Of course there might be mistakes made when deciding what the code should do, but that’s a different story. Unit testing also makes code easier to maintain and further develop.
To be able to unit test code, the code needs to be unit testable. This usually also means the code is cleaner (clean as in Clean Code) which makes it easier to understand and change the code. And when the code is covered with good set of unit tests, it is also safe to change the code. Every code written has a price. There’s a price to develop the code, but there’s (often even larger) price to maintain the code. Clean code which is covered with unit tests has a smaller price tag than code which is not that clean and/or is not covered with unit tests.
Adding unit tests to code is boring. This is true. And if the code will not be further developed, it is complete waste of time as well. Unit tests do not add much (or any) value when written afterwards, specially if long time has passed since the code to be tested was written. As said, adding unit tests to code which was not written to be unit testable in the first place is laborious and often requires big refactorings to be made before unit testing can take place. And as there are no unit tests to cover poor developer’s ass, those refactorings might break things really badly. Luckily there are good old books to help in tasks like this. Do read Martin Fowler’s Refactoring and Michael C. Feather’s Working Effectively with Legacy Code.
So, this far we’ve learned that unit tests often don’t add any value, are difficult to write and the whole thing is also really boring. Forget unit tests completely? No, I’ve found a nice solution which you’ve probably heard earlier as well. It’s called test-first programming or test-driven development (TDD). I personally like most the term red/green/refactor. After I learned to do TDD (as if I meant it) I’ve enjoyed writing code a lot more. Nowadays I don’t often get to write code, but when I do, I use TDD and I love it.
And even if you didn’t like TDD or don’t want to try it (if this is so, I’d like to know why), you can still add the unit tests while you’re writing your code. Then you must think about unit testability before you write the first line of production code. Code design must be done so that adding unit tests is easy.
As a final note, consider Martin Fowler’s words and think about this the next time you’re writing code:
Whenever you are tempted to type something into a print statement or a debugger expression, write it as a test instead.