CheckController tests have uneeded cases and are missing checks

[puffitos]

Is there an existing issue for this?

• I have searched the existing issues

Current Behavior

The CheckController has some tests which aren't checking anything and are only running a function, and some test cases are examining states which cannot happen (like registering a duplicate check and removing a non-existing check).

Expected Behavior

Tests only check real states and do check if something happened.

Steps To Reproduce

No response

Relevant logs and/or screenshots, environment information, etc.

No response

Who can address the issue?

Everyone

Anything else?

Pointed out by @lvlcn-t on #130