Test environment: reorganized files, split folders, ...

[k00ni]

Overview

I reorganized our test related files in a way to have a better separation of concerns. For instance, mock files were located next to test files. There are still things to do, but this PR is a good step in the right direction in my opinion. I hope the new structure makes it more clear if someone wants to fix a bug or wanna find certain test cases.

The new test-related folder structure looks roughly like this:

• root folder
  • test (new) - contains test related (helper) files, fixtures, ...
    • MockClass - contains mock classes
  • tests - contains only test-classes
    • ...
    • ParserTest/RDFa (new) - contains RDFa related test class as well as fixtures

Highlights

• separate tests from helper classes, fixtures etc.
• separate RDFa tests from parser tests (put it together with fixtures, so all RDFa related test files are together)
• separated mock classes from test classes
• introduced ROOT_PATH constant to avoid __DIR__ usages all over the place (only partly implemented yet)
• i added a few type declarations and further checks, so errors appear earlier than before if something went wrong (e.g. a fixture could not be loaded)
  • example: https://github.com/sweetrdf/easyrdf/blob/feature/reorganized-tests/tests/ParserTest/RDFa/RdfaTest.php#L53-L77

[k00ni]

I would like to hear your opinion on the general direction of these changes, if you can spare the time.

CC @zozlak @claudiu-cristea @idimopoulos