Add mock-based unit tests for ExchangeRateProvider

[gcomte]

Summary

• Add 5 offline unit tests using a mock ExchangeRateApiConsumer
• Tests cover: inverse calculation, caching (fetch called once), missing currency panic, zero rate → infinity, multi-currency lookups
• No network dependency — these run reliably in any environment

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 20c139f9-2207-4137-b4a2-1d5eb76e5f5f

📥 Commits

Reviewing files that changed from the base of the PR and between 0fc0ae0 and 9a19b6c.

📒 Files selected for processing (1)

• src/fiat_rates/exchange_rate_provider.rs

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📝 Walkthrough

Walkthrough

A test module was added to src/fiat_rates/exchange_rate_provider.rs containing a mock implementation of ExchangeRateApiConsumer and unit tests validating ExchangeRateProvider behavior, including caching, rate calculations, and edge cases.

Changes

Cohort / File(s)	Summary
Test Module Addition src/fiat_rates/exchange_rate_provider.rs	Added #[cfg(test)] test module with MockApiConsumer mock and five unit tests covering btc_value return logic, API caching behavior, missing currency handling, zero rate edge cases, and multiple currency support.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~5 minutes

Poem

🐰 Tests hop in with bounds so fine,
Caching logic checked line by line,
Mocks and assertions, all aligned,
No production code redesigned! ✨

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 66.67% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The pull request title accurately describes the main change: adding mock-based unit tests for the ExchangeRateProvider class.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/add-mock-exchange-rate-tests

Warning

Review ran into problems

🔥 Problems

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