[TESTING] Add BTT tests for diamond module, inspect & upgrade facets/modules

[maxnorm]

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Testing Issue

Help us improve our test coverage and quality:

Description

Add behavior-driven tests (BTT/fuzz + edge-case behavior checks) for the diamond internal module and related inspect/upgrade facets.
These files implement core selector import/validation, facet linked-list bookkeeping, add/replace/remove upgrade flows, fallback dispatch, and introspection views. They are security-critical and currently appear to have no dedicated tests.

The new tests should validate happy paths, revert paths, list-link integrity, selectorCount/facetCount invariants, and introspection correctness after multi-step upgrades.

Target File/Function(s) being tested

• src/diamond/DiamondInspectFacet.sol
• src/diamond/DiamondMod.sol
• src/diamond/DiamondUpgradeFacet.sol
• src/diamond/DiamondUpgradeMod.sol

Suggested coverage focus:

• invalid selector encoding / no bytecode / no selectors reverts
• duplicate selector conflicts on add
• replace with same facet, replace non-existent facet, replace with selector ownership conflicts
• remove non-existent facet
• head/tail relinking correctness when replacing/removing first, middle, and last facets
• selectorCount/facetCount invariants across sequences of add→replace→remove
• delegatecall bubbling + DiamondDelegateCall and DiamondMetadata event behavior
• introspection consistency (facetAddresses, facets, facetFunctionSelectors) after each upgrade step

We aim the full coverage when possible

Helpful Information

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[megabyte0x]

would like to work on this, if still relevant and required.

[maxnorm]

Heyy @megabyte0x,

Yes, it's still relevant! Most test are done for the library except the core part from the new ERC8153 implementation.

Please review our testing approach before. If you have any quesitons or suggestions, please don't hesitate.

[maxnorm]

@megabyte0x Hi, i just want to confirm you're still interested in this issue?

[megabyte0x]

Hey

I am still interested, but I'll be able to start after a week, my laptop is in repair shop.

[maxnorm]

@megabyte0x

Sorry for your laptop. Hope it's not too bad.

No worries, this task is yours. Take the time needed.

If you have any questions, reach out

[megabyte0x]

Hey
Will start work on this today.

[maxnorm]

Heyy @megabyte0x, just doing a quick follow up on this