Set up IO testing for persistence

[uliSchuster]

Testing persistence requires IO. To test it, we need to interface the application that performs persistence operations with the persistence engine. Ideally, we can target both a mock and a real persistence engine. Therefore, this issue is also to figure out how to mock the persistence engine.

Acceptance criteria:

• There is a test suite with an initial test that writes and reads from the persistence store
• The test suite can be targeted at a mock and at an actual persistence engine
• There is a simple mock in place.
• All tests pass.