[WIP] Added basic CRUDControllerTest

Code coverage of SonataAdmin after merging this PR:
 - Lines: 50.41%
 - Functions and Methods: 51.82%
 - Classes and Traits: 43.33%

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -