Remove the dependency with the sample data in the tests

[hynnot]

We depend on the tests with the sample data; if this sample data were to change, the tests would fail. We should try to remove this dependency by providing the data necessary to test the behavior in the tests themselves and, ideally, leaving the database clean again.

To provide this data, we could make a factory with different input parameters to create the data needed. We could start by refactoring these newly created tests: #921