is it ok to write test cases for save/update/persist methods - weather it be mock or by calling real methods

I have code set up in which there are different projects - like multi module maven projects.

We are setting up the sonar reports and code coverage reports.

So to start with , we have written the test cases for various layers - like BUsiness layer , common layer , Batch layer, Services Layer , Data layer.

Data layer - is the module where we do all the DB operations - like look up, save, persist, update and merge.

I have searched a lot - but there are no subtle discussion around these topics.

is it ok to write test cases for save/update/persist methods - weather it be mock or by calling real methods ..?

Any comments are welcome, thank you in advance...