You've chosen a difficult section, the data layer to want to test.
Generally you will have to design for testability, specifically having a datamanager class which does the logics and have some protected method for just storing and readling e.g. then you can derive that class and implement a ram instance for your unit testing purposes.
This describes the principles in play and it what you need to make your own practice before you can begin to mock out data layer components.
another aspect is the ability to 'mock out' certain calls (alternatively) here a lot of provider ways are available but see a good article here http://www.codeproject.com/Articles/686935/Unit-testing-with-Mock-objects-Rhino-Mocks