More unit tests and integration tests #45
Description
Currently, there are very few tests.
The collection game service is really the only service that is covered by unit tests.
We don't need 100% code coverage just for code coverage sake, but having more tests would be nice.
For testing with EntityFramework, I suggest using an InMemory database, I already implemented this for the collection game service. Maybe the TestDbContextFactory should be moved to Tests.Common and be used for all service tests.