So I gave a talk at the Edmonton .NET User Group on an introduction to automated testing. And of course in this introduction I gave a list of reasons why unit testing is a good idea. Although there are already many blog posts other there on this subject, I thought I’d record my reasons here.
Although all of these reasons may appeal to your hipster, idealistic sense of craftsmanship and professionalism, each of these reasons also has a sound business foundation. Automated testing saves/makes you money.
1. Product Quality
Of course the most obvious reason for automated testing is to improve product quality. Although automated testing will not guarantee that you’ll never have another bug, it will lower that bug rate. And having working software is the #1 design goal. Telling customers about the automated testing that is in place can be a strong marketing point.
Nobody will buy software that doesn’t work.
2. Because you are doing it anyway
If you aren’t doing automated testing, then you are doing manual testing. Manual testing (and all testing) is a thankless job that doesn’t get the credit it deserves. A lot of people assume it just happens for free.
Manual testing does take a lot of time and effort. To run a test takes a lot of time just to set up. For example, confirming how the system behaves with a customer with bad credit. You have to create or find a customer record and change its credit status. Once the setup is done comes the actual testing. You have to run the program, login as the customer, and attempt to make a purchase. This all takes time, several minutes.
Setting up an automated test also takes quite a bit of time. This is especially true for the first test. However the good news is you only have to do this once. Once the test is written you can run it as often as you want, several times an hour typically. Also running the test is much faster; no having to start the program, login, and all the other typing and button clicks. And the code you write to setup your first test will be reused for all the other tests.
Although the first test is the most difficult to write, before the first production build of your program the time spent building an automated test suite will be less that then time it takes to manually test the same program once. And once the automation is in place, it can be run whenever virtually instantaneously.
Automated testing takes less time than manual testing. This is certainly true in the full lifecycle of the program, but is even true before the first production release.
3. Enables Refactoring
Refactoring is the practice of going back over existing code and improving the readability of it. It removes technical debt.
A common practice on my team is doing code reviews, especially with new hires. The result of code review is often a list things that should have been done differently. On receiving these suggestions the programmer asks, should I implement those changes. The answer is, it depends.
If the testing has been done manually then the answer is often “no”. The code review is at the end of the project and we are up against a deadline. Although the changes may be fairly simple, the effort to manually retest the program does not out weight benefits of the cleaner code. It is usually just too risky to change the program.
This is true not only for the first release, but future maintenance cycles. When other developers go into the same code base and need to make a minor enhancement. The risk that changing the program will introduce a bug is too high.
Furthermore, having a single program contain two design styles is a sin unto itself. New features will likely be implemented following the example of the design already in place. The bad design will perpetuate. This is similar to the Broken Windows Theory. The code begins to rot. Eventually it reaches the point where the only course of action is to throw the existing code away and begin a full rewrite.
However, if the program supports an automated test suite the answer to if the code should be improved is usually “yes”. The very first time I used unit testing we did the normal code review process and the experience was completely different than previously. Even though the code review was done only hours before the deadline, most of the suggestions were implement before the release. This was because changes could be made without the penalty of a long testing cycle and risk of introducing a bug.
The quality of code for a program without unit tests will only degrade over time. A program with unit tests will improve in quality over time. This improves the longevity of the program and avoids “the big rewrite”.
4. Better Design
This point is a little controversial, but in general unit testing will improve the design of a program. Code that is testable will be designed to be smaller. It will yield code that better follows the Single Responsibility Principal. It will be less coupled to other parts of the system and have better reuse potential.
Here is an excellent video by Michael Feathers on why and how unit testing encourages good design: https://vimeo.com/15007792. It states it much better than I can.
The counter argument is that sometimes this can cause systems to become over designed. This point was made by David Heinemeier Hansson in a blog post. This caused much debate on the internet, some of which was captured here between David and Kent Beck in this 5 part video series.
At the end of the day, the programmer is in control of the design of the system. Doing Test Driven Development is a tool that helps with design, but it does not take away decisions from the programmer. Automated testing forces programmers to think more diligently about design and makes them better designers.
5. Quicker Feedback Loop
Staying in “the zone” is critical to being productive while developing software. There are dozens of pieces of information and background context that need to be kept in mind while programming. When you switch from one task to another there is a productivity drop of 20%.
With manual testing often the developer implements a feature, compiles it a week later, it sits in the tester’s inbox for a week, tested, then the test results get analyzed by the developer a week later. It is common there is a 2 or 3 week gap between implementation and the time you need to fix it. When the test results are received it can take hours to reproduce the issue and find the offending line of code.
With unit testing the workflow is write a line or two of code, then run the tests. When a test fails it is simple to remember the line of code that caused the bug. That’s because you just wrote that line of code a minute ago.
Unit testing takes the debugging process from an hour or more to a minute or less. Unit testing adds productivity due to the short feedback loop.
6. Team Ownership
The great thing about automated testing is that once the test is created it is saved and shared with the entire team. Every other team member pull in that test when they do their testing.
If a developer implements another user case scenario that is in conflict with existing features the automated tests will reveal this immediately. All developers on the team must support all the features of the system, not just the small part of the system they are working on.
Automated testing ensures that older tests are always run (i.e. regression testing). This prevents breaking changes from affecting existing customers. It improves communication on the team because all these cases are known.
7. System Documentation
With all development, but especially with APIs, providing working examples of how the code should be called and what the expected results are is important. Automated tests can provide these examples.
Also the automated tests will never become stale like a English document may become. The tests are guaranteed to stay current with the production code because they are run with every build.
Manual testing is a boring, tedious job. Running the same test scripts over and over again is mind numbing. What is boring and tedious should be automated. This is what computers are good at.
Most developers find the challenge of automating testing to be enjoyable. Asking employees to do a job that is boring will likely cause them to quit.
And also, it is no fun having customers yell at you because the software doesn’t work. Bugs lead to blame. Blame leads to fear. Fear leads to anger. Anger leads to hate. Hate leads to suffering. ~Yoda
Automated testing decreases employee turnover.
9. Required Skill
When getting started with automated testing (or any new technology or process) there will be resistance. You will hear the fallacies that it will take too long, its too hard, or it will hurt the design. Whatever the reasons you have for not doing automated testing, don’t let that you don’t know how be one of them.
The harshest critic of automated testing will still conceded that in some circumstances it is still proper thing to do. Therefore when the time comes that testing should be automated ensure that you and your team are proficient in doing so. It is a skill that can only be learned from practice.