fatkodima/data_checks: Regression testing for data

Making sure that data stays valid is not a trivial task. For simple requirements, like "this column is not null" or "this column is unique", you of course just use the database constraints and that's it. Same goes for type validation or reference integrity.However, when you want to check for something more complex, then it all changes. Depending on your DBMS, you can use stored procedures, but this is often harder to write, version and maintain.