In the ovverride of tryPauseAutoCompactForReplicaSetWritesBlock, the StorageEngineMoch returns an error status rather than throwing, so the new test does not exercise the observer helper's DBException catch. Removing that catch would still pass the test, although an escaping exception would terminate the process through RecoveryUnit::Change::commit() noexcept.

As part of this ticket, we should make this mock throw so the existing commit and write-block-state assertions verify that exception handling, not just a returned failure status.