[WIP] refactor mock-based testing rpc_interface.rs

[roypat]

This was the easiest way to see the impact of this experiment in codecov's nice UI, sorry

Changes

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Reason

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License Acceptance

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PR Checklist

• [ ] If a specific issue led to this PR, this PR closes the issue.
• [ ] The description of changes is clear and encompassing.
• [ ] Any required documentation changes (code and docs) are included in this PR.
• [ ] API changes follow the Runbook for Firecracker API changes.
• [ ] User-facing changes are mentioned in CHANGELOG.md.
• [ ] All added/changed functionality is tested.
• [ ] New TODOs link to an issue.
• [ ] Commits meet contribution quality standards.

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• [ ] This functionality cannot be added in rust-vmm.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 84.37%. Comparing base (bd18d01) to head (8ddf9e9). Report is 13 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4646      +/-   ##
==========================================
- Coverage   84.38%   84.37%   -0.02%     
==========================================
  Files         249      249              
  Lines       27452    27452              
==========================================
- Hits        23165    23162       -3     
- Misses       4287     4290       +3     

Flag	Coverage Δ
5.10-c5n.metal	84.60% <ø> (-0.02%)	:arrow_down:
5.10-m5n.metal	84.58% <ø> (-0.02%)	:arrow_down:
5.10-m6a.metal	83.87% <ø> (-0.02%)	:arrow_down:
5.10-m6g.metal	80.94% <ø> (+0.02%)	:arrow_up:
5.10-m6i.metal	84.57% <ø> (-0.02%)	:arrow_down:
5.10-m7g.metal	80.94% <ø> (+0.02%)	:arrow_up:
6.1-c5n.metal	84.60% <ø> (-0.02%)	:arrow_down:
6.1-m5n.metal	84.58% <ø> (-0.02%)	:arrow_down:
6.1-m6a.metal	83.88% <ø> (-0.01%)	:arrow_down:
6.1-m6g.metal	80.94% <ø> (+0.03%)	:arrow_up:
6.1-m6i.metal	84.57% <ø> (-0.02%)	:arrow_down:
6.1-m7g.metal	80.94% <ø> (+0.02%)	:arrow_up:

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[roypat]

Just to confirm, so unit/integ tests don't cover every variant of the match statement?

If the match arm is of the form Action::Something(bla) => other_function_with_unittests(bla), then no, I didn't consider that very useful. More complex cases are exercised by the rust integration tests now