Top Five Excuses For Not Unit Testing

Paul Bourdeaux  |  April 16, 2009

People who don’t unit test always seem to have an excuse why. Some of them are understandable misconceptions about unit testing. Some of them are ridiculous. But I have yet to hear an excuse that I would consider valid. Here are the top five excuses I hear, and my responses to them.

I don’t have time to unit test.
Really? But you have to time to fix your mistakes later? The simple fact is that nobody, not even you, can write bug free code. Unit tests greatly speed up the time it takes to identify a bug because they narrow the suspect code down to a very specific unit. Other types of testing, such as Quality Assurance or User Acceptance Testing, identify problems at a much higher level, forcing the developer to spend extra time plodding through the various units looking for the root cause. Unit tests can also serve as verification that the bug is corrected without having to go through the hassle of creating a new application build and deploying it for further testing. Simply put, unit tests speed up overall development. It might take slightly longer to create each new feature, but the development time for the entire application, from inception to delivery, is considerable shorter.
The client pays me to develop code, not write unit test.
News Flash - Unit tests are code. They are as integral to the application as any other piece of code you are writing, and should be included in the original estimate and statement of work. It might also help to mention to the client that unit tests lower both development cost (see previous excuse) as well as maintenance cost. If you are not writing unit tests, then you are doing your client an injustice by forcing them to incur extra expense.
I am supporting a legacy application without unit tests.
That still doesn’t preclude you from writing your own. Granted, you are not going to be able to go in and write tests to bring the entire code base up to an acceptable level of coverage. You most likely don’t have the time or resources to do that. But as support issues are raised, write the unit tests for any code that you modify. When I am working on a support task, one of the very first things I do is write a unit test to recreate the bug. When the unit test starts passing, I know that I have fixed the problem. Now, not only have I resolved a bug, but I have added some unit test coverage to the code base. Over time, this coverage will become more and more robust, and actually reduce future maintenance costs by preventing the introduction of regression bugs.
QA and User Acceptance Testing is far more effective in finding bugs.
No arguments there. But Unit Testing is far more effective at preventing bugs. Just because my smoke alarm is better at detecting potential fires doesn’t mean that it is safe to leave the stove on all the time. QA and UAT are smoke alarms - they alert you to potential existing trouble. Unit testing is turning off the stove when you are done - it helps you prevent trouble. Unit testing, QA, and UAT are all important parts of the testing process, and they each play very different roles. Trying to replace one with another doesn’t work. I wouldn’t release a project that was well unit tested without QA, and I wouldn’t release a project that was thoroughly QA’ed without unit testing.
I don’t know how to unit test, or I don’t know how to write good unit tests.
Well, this is probably the most valid excuse that is out there. The sad truth is that a great many number of developers and engineers do not know how to unit test. I didn’t when I started. And nothing discourages a developer more than struggling to write bad unit tests. Luckily there are resources out there. There are so many books, webinars, conference presentations, blogs, etc on writing good unit tests that the inability to write them simply isn’t going to cut it as an excuse any more. When someone offers me this excuse, I don’t look at it as a roadblock, but rather as a teachable moment. It usually only takes a time or two of seeing how well written unit tests can help one develop code to turn them from the dark side…

Are there other excuses out there? Absolutely. But they are just that - excuses. I have yet to encounter a valid reason to skip unit testing. If you think you have one, post it here. I look forward to the challenge of changing your mind!

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