Unitests for services

We need to find a way for service-level unit tests.

For now, we only have integration tests, but it only defined the shared behavior for our services.

go-service-qingstor uses gomock, but it’s hard to maintain and verify. Here is a plan for it to remove the mock: Migrate unittests into integration tests, remove the mock · Issue #50 · beyondstorage/go-service-qingstor · GitHub