BE-UT has actually been configured to ignore access control, so it can access all private interfaces.
#includes a be/src .cpp (to reach file-static helpers) must have that file opted out of unity batching via doris_skip_unity_inclusion in the owning be/src/.../CMakeLists.txt — otherwise the batch object‘s copy of the definitions collides with the test’s inlined copy and the BE UT link fails with duplicate symbols. Enforced at configure time by build-support/check-unity-skip-coverage.py; its error message names the exact entry to add. Prefer not including .cpp files at all when the code can be exercised through a header.