There is currently some test coverage of the index timestamping logic provided by StorageTimestamp dbtest suite and the rollback fuzzer. It would be beneficial to gather all the timestamping test cases in a single unit test to set expectations on how the various phases of an index build are timestamped.

This work was proposed during a discussion on SERVER-39085 and will provide additional confidence as we transition the server index builds to the IndexBuildsCoordinator.