feature(gRPC): add tests #9621
Description
Currently the tests mostly check the "read masks".
We should go through all endpoints and add test cases for example for "missing data" in the backend, or every other possible edge case, to test the full functionality, not only in the "happy-case".
These tests should be e2e tests. While we implement the tests, we should make sure that we are using the client functions, instead of the gRPC proto types directly, to test the full path.