test(profile): add credits.rs coverage for spend/earn/refund/admin_grant

[Sendi0011]

Summary

Adds tests/credits.rs for contracts/profile/src/credits.rs, covering
bootstrap, spend, earn, refund, and admin_grant.

Closes #26 (part of #25).

Coverage

• Happy path for each function
• Every Error variant actually reachable from credits.rs:
  EventsContractNotConfigured, OpAlreadySeen, Paused,
  ProfileNotFound, InsufficientCredits, ReasonRequired
• Edge cases: zero-amount spend, exact-balance spend to zero, u32::MAX
  saturation on earn/refund/admin_grant, admin_grant bootstrapping
  a fresh profile for an unknown user
• Idempotency: replayed op_id rejected on every function, including the
  zero-amount spend no-op path
• Auth rejection: bootstrap/spend/earn/refund reject a caller that
  isn't the configured events contract; admin_grant rejects a caller
  that isn't admin. These use mock_auths + #[should_panic] since
  require_auth() panics rather than returning an Error — there was no
  existing auth-rejection test anywhere in the suite to follow, so this
  establishes the pattern.

Note: Error::InvalidAmount is declared in errors.rs but is never
returned by any path in credits.rs, so it isn't tested here — happy to
add if it's meant to be wired in as part of this issue.

Testing

```
cargo test -p boundless-profile
cargo test
```

Screenshot

Summary by CodeRabbit

• Tests
  • Added comprehensive test coverage for the credits system, including bootstrap, spend, earn, refund, and admin grant operations with edge case handling and error scenarios.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 72b7199a-6840-41e8-825e-eff0700d4a82

📥 Commits

Reviewing files that changed from the base of the PR and between d3a32bd and 03dd912.

📒 Files selected for processing (2)

• contracts/profile/src/tests/credits.rs
• contracts/profile/src/tests/mod.rs

---

📝 Walkthrough

Walkthrough

Adds contracts/profile/src/tests/credits.rs, a 762-line test suite covering bootstrap, spend, earn, refund, and admin_grant operations in the profile credits contract. Each operation is tested for happy paths, edge cases (saturation, zero-amount), every error variant, and auth-rejection panics. The module is registered in tests/mod.rs.

Changes

Credits Contract Test Suite

Layer / File(s)	Summary
Test scaffolding and bootstrap tests contracts/profile/src/tests/mod.rs, contracts/profile/src/tests/credits.rs	Registers the new credits submodule and adds imports, shared op_id helper, and bootstrap tests covering default credit initialization, bootstrapped_at assignment, idempotency, replay rejection, missing events config, paused state, and non-events-contract panic.
Spend operation tests contracts/profile/src/tests/credits.rs	Covers credit deduction, zero-amount no-op with op_id still marked as seen (replay rejected), insufficient-credit revert with no state change, unbootstrapped-user revert, replay rejection, paused and missing-events-config reverts, and non-events-contract panic.
Earn, refund, and admin_grant tests contracts/profile/src/tests/credits.rs	Covers earn (saturation to u32::MAX, error variants, auth panic), refund via spend-then-refund workflow (saturation, same error variants), and admin_grant (bootstrap-on-unknown-user, saturation, empty-reason revert without profile creation, replay rejection, paused revert, non-admin panic).

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related issues

• #26 (test(profile): credits — spend / earn / refund / admin_grant): This PR directly implements the acceptance criteria by adding tests/credits.rs covering all five operations with happy paths, every Error variant, edge cases, and auth-rejection tests, and wires it into tests/mod.rs.
• #30: The PR's earn tests in credits.rs overlap with the requested earnings-specific coverage, though the organization differs (a combined file rather than a dedicated earnings.rs).

Poem

🐇 Hoppity-hop through the credit lanes,
Bootstrap and spend with no replay pains,
Earn to the max where u32 ends,
Refund the credits the contract defends,
Admin may grant but must know the reason—
All tests now pass in every season! ✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately summarizes the main change: adding comprehensive test coverage for the credits module's spend/earn/refund/admin_grant functions.
Linked Issues check	✅ Passed	The PR fully satisfies issue #26 requirements: new tests/credits.rs covers all functions (bootstrap, spend, earn, refund, admin_grant) with happy paths, error variants, edge cases, idempotency, and auth-rejection testing; all 49 tests pass.
Out of Scope Changes check	✅ Passed	All changes are in-scope: adding tests/credits.rs test suite and a single mod declaration in tests/mod.rs, both directly supporting the test coverage objectives.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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