Add test to check the value of "prefix"

[curquiza]

Following this issue (#12) and this PR (#13), we need to add test checking the value of prefix (in meili_search.yml file), especially testing the empty value.

Any suggestions to implement these tests?

[codedge]

There seems to be an existing test to check if an index could be cleared - https://github.com/meilisearch/meilisearch-symfony/blob/main/tests/TestCase/CommandsTest.php#L66

Anything else that should be tested in this ticket here or can this be closed?

[curquiza]

Indeed!! Closing :)