Testing is one of the most important tasks of writing softwares, but most developers or programmers pay less attention in this part. However, every product, such as commercial products, must be tested before they are released to the world.

The simplest way to write testing code is to write the print statement in your code. By being a little bit more creative, you could create your own method, let's say "assert", and let every method call it. It is obvious that your testing has limitations. For instance, when you want to turn off your testing, you have to comment those print statements out! Think about it if you have a thousand lines of code. You don't want to do that, do you? And another problem is that your code is not scalable. When you add more lines of code, you have to add more print statements, right?

There are many kinds of testing and the well-known one is "Unit Testing". You can read the information about it more here.

I won't write anything about it because I think the reference above already explains it explicitly.

By the way, how do we write testing code?

Nowadays, we don't need to. Why? Because many developers do for us. Many frameworks and tools of testing you can use are out there.

I have found this site, Opensourcetesting.org. I think it would be very very useful certainly for developers; so, we should change our old attitudes that testing is boring or something and intend to study it.