Node: Documentation about tests

[italoacasas]

I notice that we don't have any documentation about tests. But is something that is going to be really helpfully to have for new contributors like myself. Maybe someone with the knowledge can add some introduction like, folder struct, some basic examples, etc...

@nodejs/documentation

[vsemozhetbyt]

There is a start.

[gibfahn]

The test README has some info about the folder structure, although it's pretty new.

@santigimeno: your test guide is very helpful, but would it be helpful to add that tests should have a comment section giving brief documentation? Most of the tests don't really have any documentation of what they actually test.

[santigimeno]

would it be helpful to add that tests should have a comment section giving brief documentation?

@gibm Yes, I completely agree with you. Sometimes it's difficult to figure out what the test is really _testing_.

[santigimeno]

Also, documenting the test/common.js API would be a great addition.

[jasnell]

This has been done