5 Reasons why you should test your code

It is just like in mathematics class when I had to make a proof for Thales’ theorem I wrote “Can’t you see that B has a right angle?! Q.E.D.”, but he still gave me an F grade.
You want to make things work, right? So you start programming until your feature is implemented. When it is implemented, it works, so you do not need any tests. You want to proceed and make more cool features.
Suddenly feature 1 breaks, because you did something weird in some service that is reused all over your application. Ok, let’s fix it, keep refreshing the page until everything is stable again. This is the point in time where you regret that you (or even better, your teammate) did not write tests.
In this article I give you 5 reasons why you should write them.

1. Regression testing

The scenario describes in the introduction is a typical example of a regression bug. Something works, but it breaks when you are looking the other way.
If you had 100% code coverage, a red error would appear in the console or – even better – a siren would go off in the room where you where working.
Although there are some misconceptions about coverage, it at least tells others that there is a fully functional test suite. And it may give you a high grade when an audit company like SIG inspects your software.

100% Coverage feels so good

100% Code coverage does not mean that you have tested everything.
This means that the test suite it implemented in such a way that it calls every line of the tested code, but says nothing about the assertions made during its test run. If you want to measure if your specs do a fair amount of assertions, you have to do mutation testing.
This works as follows.
An automatic task is running the test suite once. Then some parts of you code are modified, mainly conditions flipped, for loops made shorter/longer, etc. The test suite is run a second time. If there are tests failing after the modifications are made, there is an assertion done for this case, which is good.
However, 100% coverage does feel really good if you are an OCD-person.
The better your test coverage and assertion density is, the higher probability to catch regression bugs. Especially when an application grows, you may encounter a lot of regression bugs during development, which is good.
Suppose that a form shows a funny easter egg when the filled in birthdate is 06-06-2006 and the line of code responsible for this behaviour is hidden in a complex method. A fellow developer may make changes to this line. Not because he is not funny, but he just does not know. A failing test notices him immediately that he is removing your easter egg, while without a test you would find out the the removal 2 years later.
Still every application contains bugs which you are unaware of. When an end user tells you about a broken page, you may find out that the link he clicked on was generated with some missing information, ie. users//edit instead of users/24/edit.
When you find a bug, first write a (failing) test that reproduces the bug, then fix the bug. This will never happen again. You win.

2. Improve the implementation via new insights

“Premature optimalization is the root of all evil” is something you hear a lot. This does not mean that you have to implement you solution pragmatically without code reuse.
Good software craftmanship is not only about solving a problem effectively, also about maintainability, durability, performance and architecture. Tests can help you with this. If forces you to slow down and think.
If you start writing your tests and you have trouble with it, this may be an indication that your implementation can be improved. Furthermore, your tests let you think about input and output, corner cases and dependencies. So do you think that you understand all aspects of the super method you wrote that can handle everything? Write tests for this method and better code is guaranteed.
Test Driven Development even helps you optimizing your code before you even write it, but that is another discussion.

3. It saves time, really

Number one excuse not to write tests is that you do not have time for it or your client does not want to pay for it. Writing tests can indeed cost you some time, even if you are using boilerplate code elimination frameworks like Mox.
However, if I ask you whether you would make other design choices if you had the chance (and time) to start over, you probably would say yes. A total codebase refactoring is a ‘no go’ because you cannot oversee what parts of your application will fail. If you still accept the refactoring challenge, it will at least give you a lot of headache and costs you a lot of time, which you could have been used for writing the tests. But you had no time for writing tests, right? So your crappy implementation stays.

A bug can always be introduced, even with good refactored code. How many times did you say to yourself after a day of hard working that you spend 90% of your time finding and fixing a nasty bug? You are want to write cool applications, not to fix bugs.
When you have tested your code very well, 90% of the bugs introduced are catched by your tests. Phew, that saved the day. You can focus on writing cool stuff. And tests.
In the beginning, writing tests can take up to more than half of your time, but when you get the hang of it, writing tests become a second nature. It is important that you are writing code for the long term. As an application grows, it really pays off to have tests. It saves you time and developing becomes more fun as you are not being blocked by hard to find bugs.

4. Self-updating documentation

Writing clean self-documenting code is one if the main thing were adhere to. Not only for yourself, especially when you have not seen the code for a while, but also for your fellow developers. We only write comments if a piece of code is particularly hard to understand. Whatever style you prefer, it has to be clean in some way what the code does.
  // Beware! Dragons beyond this point!
Some people like to read the comments, some read the implementation itself, but some read the tests. What I like about the tests, for example when you are using a framework like Jasmine, is that they have a structured overview of all method’s features. When you have a separate documentation file, it is as structured as you want, but the main issue with documentation is that it is never up to date. Developers do not like to write documentation and forget to update it when a method signature changes and eventually they stop writing docs.
Developers also do not like to write tests, but they at least serve more purposes than docs. If you are using the test suite as documentation, your documentation is always up to date with no extra effort!

5. It is fun

Nowadays there are no testers and developers. The developers are the testers. People that write good tests, are also the best programmers. Actually, your test is also a program. So if you like programming, you should like writing tests.
The reason why writing tests may feel non-productive is because it gives you the idea that you are not producing something new.

Is the build red? Fix it immediately!

However, with the modern software development approach, your tests should be an integrated part of your application. The tests can be executed automatically using build tools like Grunt and Gulp. They may run in a continuous integration pipeline via Jenkins, for example. If you are really cool, a new deploy to production is automatically done when the tests pass and everything else is ok. With tests you have more confidence that your code is production ready.
A lot of measurements can be generated as well, like coverage and mutation testing, giving the OCD-oriented developers a big smile when everything is green and the score is 100%.
If the test suite fails, it is first priority to fix it, to keep the codebase in good shape. It takes some discipline, but when you get used to it, you have more fun developing new features and make cool stuff.