Testing in general is a process that is normally left really in a partial state. The problem with this fact is it normally leaves things up to users or testers to find. And then, once found, the cost to fix the bug could be huge and hypothetically speaking, could touch various other parts of the application.
This is where unit tests and integration tests come in handy! Since this is a fairly broad topic, I am going to start by just talking about Unit Tests.
By definition, unit testing is a software testing method by which individual units of the source code are tested to determine whether they are fit to use.
So let's start from the beginning. What is a unit? It is the smallest testable part of an application. In procedural programming this could be an entire function, or as much as an entire page / section of code. In object oriented programming, these either an interface, or could even be a class.
But writing unit tests is still me writing code how will it help in the long run since it's taking away from the development of my site? It will help in the long run. I've had several occasions come up when I go to change "one small thing" which then ripples through and breaks other pages that touch this one unit. Essentially you are building your first layer of protection against future potential bugs.
The nice thing about writing test cases is it also allows you test things that may occur on the fringe cases. This will help to ensure that everything will should act as it's supposed to even in the strangest of situations. One of my favourite testing strategies (although admittedly I rarely do it), is actually test driven development. With Test Driven Development, you start coding by knowing what you want the end result to be (for your unit of work). You actually write tests for it and expect it to fail. If it doesn't fail right out of the gate, then your test may not actually be doing anything/finding anything useful. Then as you work your way through the development of this unit, you run your tests. Are all of your tests passing? If they aren't, then you know that you still have some work to do. However, if everything passes, then you know your application should work for at least all of your known cases. Which if you set up your tests correctly, should give you good confidence in the code.
The nice thing about writing these unit tests is that once you find a bug in any environment and resolve it, you are then able to actually write a unit test in order to actually test for that case so, if you change some more code, you don't re-introduce that bug.
With PHP, I, like most people, use PHPUnit as the primary unit testing software. Not only because it's built into Laravel and Laravel actually has helpers built on top to make the testing process even easier!
Although writing these test cases can sometimes be a big pain in the butt, if you do it correctly it can help you to spot issues earlier on in development before the time when it is "too late".
Hopefully this comes in handy for you!
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