[FEATURE] refactored to new api

__Tasks:__
- [x] refactor all REST-Controllers to meet the new API conditions
- [ ] gather feedback for my changes 

__Informations:__

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| Tests pass?   | none
| Fixed tickets | [none]
| Doc           | none
You can replace `assertEquals` with `assertCount`:

````php
$this->assertCount(2, $resplonse->_embedded->groups);
````