[FEATURE] Stabilizing code coverage

## Expected behavior
Code coverage should not changed on files not concerned by a commit.

## Actual behavior
Some tests are based on random instance generation and so some part of the code is called for a commit and not for another.

## Possible Solution
Every part of a Java class should be tested, one way or another. The idea is to identify (with former Pull requests) the concerned classes and add tests to stabilize the code coverage rate.