When applying hexagonal architecture (ports and adapters) with access to infrastructure elements like databases is done by the mean of adapters, which are just implementations of interfaces (ports) defined by the domain. In this article, we are going to provide two implementations of the same repository port, one in-memory and another based on JPA, focusing on how to test both implementations with the same set of tests.
Context
Many software solutions usually developed in the enterprise context have some state that needs to be persisted in a durable store for later access. Depending on the specific functional and non-functional requirements, selecting the correct persistence solution can be hard to make and most likely require an Architecture Decision Record (ADR) where the rationale of the selection, including alternatives and tradeoffs, is detailed. For persisting your application state, most likely, you will look at the CAP Theorem to make the most adequate decision.