[DRAFT] What Should I Test?

The first question that one should ask when testing is what should I test? When testing it is important to make a clear plan before you start coding or otherwise you can easily get lost.
This page should be conceived as a light introduction to testing. However, the world of testing is pretty extensive you should not limit yourself to the contents of this page when testing.
Before starting to describe what should be tested it is useful to describe what should not be tested (in general)

1. Private classes or methods: In some cases, you might encounter that a method that you want to test is private, if this happens usually the right call is not to test it directly. This does not mean that the content of that method is not tested at all, you might want to try to test some of the side effects that the method or class can have on the general output.