Summary
Make a list of the gap we have in unit testing S3 extension. Write new tests to address them.

Motivation
This ticket is split from WT-8855. We are doing a code walkthrough and cleanup for the S3 extension and identifying all the gaps in the unit testing. This ticket will act as a scratchpad to list the gaps and then to write the new tests.

• Does this affect any team outside of WT?
  No

Acceptance Criteria (Definition of Done)
Unit testing gaps were identified and tests are written to cover them.