tests - ordering of the queue

[Jamesbarford]

• More tests for the queue invariants. Adding them as guardrails and as cases we can re-implement to ensure the new mechanism behaves in the same way.
• I also renamed a few things for clarity

[Kobzol]

Looks great, having more tests is always super useful. Also adding comments to the code that explain what it does, because the logic is quite complicated. Let me know if you want to modify something else, otherwise LGTM.

[Jamesbarford]

Looks great, having more tests is always super useful. Also adding comments to the code that explain what it does, because the logic is quite complicated. Let me know if you want to modify something else, otherwise LGTM.

I think for the time being I think this is enough. Presently I'm thinking that the logic from the function calculate_missing_from could be repurposed to insert unsorted data into a possible commit_queue table. I tired splitting the sort to a different step but it bloated out the PR and arguably made the logic harder to follow so I left the flow as it is and changed some variable names.