Test data model

[SecretJ12]

• Test knockout generator: fresh generation and update
• Test group generator: fresh generation and update
• Test data model: behaviour on creation and deletion

[FungOliver]

Maybe merge feature/player overview with criteria api into dev first. And then rebase this and then afterwards merge this?

[SecretJ12]

Maybe merge feature/player overview with criteria api into dev first. And then rebase this and then afterwards merge this?

Yeah tests are not finished yet, this pr draft is rather to get the tests running in the actions