Serving data to the Integration test

Question

I'm designing currently the integration tests. In the test object there are several entities and a quite complex data structure. The application is itself a modular monolith for now, but targeting to be a microservice system (one day soon). The system is far from ready, so many modules are not even designed. My question is how to design the tests?

• one approach should be to seed the data for the whole environment.
• one should be to create them for each module/test class/test case

I would like to hear some opinion about how someone managed likewise situation and what was the experience with the solution. Any idea is welcome.

I did in previous project to create data for each test case / test class where it was possible to make a common class without serious overhead.

• This is a big time expense, but isolation ensured and easier to maintain them

I did met with project where data was seeded.

• Any changes could break many tests, finding and fixing them was sometime a big problem and a lot of time