Improve test coverage of 2FA classes

What does this MR do and why?

While I was working on a refactor that involved these classes in this MR, I found that these methods did not have sufficient test coverage and I was adding tests for them as I refactored them.

This MR adds test coverage by adding unit tests and making all non-public methods private.

Screenshots or screen recordings

These are strongly recommended to assist reviewers and reduce the time to merge your change.

How to set up and validate locally

This MR does not have any functional changes (it is a refactor / spec update only)

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.