test(invoice-token): comprehensive test matrix validating Error::NotI…

[neyij]

…nit across all public entry points

Description

Added a comprehensive test matrix covering Error::NotInit behavior across all public entry points of the InvoiceToken contract.

The new test_uninitialized_methods_rejected test exercises the contract on a freshly deployed instance before initialize() is called. It verifies that all read and write methods reject with Error::NotInit and that failed invocations do not modify contract storage.

Closes #381

Type of Change

• 🐛 Bug fix (non-breaking change which fixes an existing issue)
• ✨ New feature (non-breaking change which adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to not work as expected)
• 📝 Documentation update
• 🎨 UI/UX improvement
• ♻️ Code refactoring
• ✅ Test addition or update
• 🔧 Configuration change

Checklist

• My code follows the code style of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published

Testing

Added a comprehensive unit test that invokes every public InvoiceToken entry point against a freshly deployed but uninitialized contract.

How to Test

1. Run the invoice token test suite:
   cargo test -p invoice-token
2. Deploy a fresh InvoiceToken contract instance without calling initialize().
3. Invoke each public read and write method and verify that every call returns Error::NotInit.
4. Verify that failed invocations do not write or modify any contract storage keys.

Test Coverage

• Unit tests added/updated
• Integration tests added/updated
• E2E tests added/updated (if applicable)
• Manual testing completed

Screenshots (if applicable)

Not applicable — this change adds contract unit tests and does not affect the user interface.

Additional Notes

The test covers the public read methods:

• name
• symbol
• decimals
• total_supply
• balance
• balance_batch
• allowance
• get_nonce
• invoice_id
• transfer_locked
• paused

It also covers the public write methods:

• transfer
• transfer_from
• approve
• extend_allowance
• revoke_approval
• burn
• burn_from
• mint
• mint_batch
• set_transfer_locked
• set_minter
• set_decimals
• set_paused

The test ensures that an uninitialized contract consistently rejects public operations with Error::NotInit rather than panicking or allowing unintended state changes.

For Reviewers

Please focus on:

• Code quality and readability
• Test coverage
• Security implications
• Performance impact
• Breaking changes

In particular, verify that all public entry points are covered, the expected Error::NotInit value is asserted consistently, and failed invocations leave contract storage unchanged.

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