atoum migration finishing

[SebSept]

• [DX] improve getItemByTypeName() : list available items
• rename AssignableItem test to AssignableItemTest
• adapt AssignableItemTest to phpunit

Checklist before requesting a review

Please delete options that are not relevant.

• I have read the CONTRIBUTING document.
• I have performed a self-review of my code.
• I have added tests that prove my fix is effective or that my feature works.

Description

• Rename class name 'suffixed' with Test, so it runs with phpunit in ci.
• Migration to phpunit