tests: add Decimal serialization contract tests

[zensgit]

Purpose

• Add contract tests to ensure Decimal fields serialize as JSON strings, preventing JS float precision issues.

Scope

• jive-api/tests/contract_decimal_serialization.rs
  • Verifies GlobalMarketStats Decimal fields serialize as strings
  • Verifies AccountResponse Decimal fields serialize as strings (including optional fields)

Notes

• Pure tests only; no business logic change
• Complements Decimal migrations in prior PRs (api: migrate transaction/budget money types to Decimal #90, api: migrate exchange rate & market to Decimal #92)

[gemini-code-assist]

Summary of Changes

Hello @zensgit, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request enhances the robustness of the API by adding comprehensive contract tests to validate the serialization of Decimal fields. The primary goal is to ensure that these fields are consistently converted to JSON strings, thereby safeguarding against potential precision loss when consumed by JavaScript clients. This is a crucial step in maintaining data integrity across the system.

Highlights

• New Contract Tests: Introduced new contract tests specifically for Decimal serialization within the jive-api to prevent JavaScript float precision issues.
• Decimal Field Serialization: Ensures that Decimal fields in GlobalMarketStats and AccountResponse are serialized as JSON strings, maintaining precision.
• Specific Field Handling: Added an explicit check for the updated_at field, confirming it serializes as a numeric Unix timestamp (i64) rather than a string, as it's an exception to the general Decimal string serialization rule.
• Test-Only Changes: These changes are purely for testing purposes and do not introduce any modifications to existing business logic, complementing prior Decimal migration efforts.

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[Copilot]

Pull Request Overview

This PR adds contract tests to verify that Decimal fields in API responses are serialized as JSON strings rather than numbers, which prevents JavaScript floating-point precision issues. This is part of a broader effort to ensure consistent Decimal handling across the API.

Key Changes

• Added test assertions for GlobalMarketStats to verify Decimal fields serialize as strings
• Added explicit verification that the updated_at timestamp field remains numeric

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[gemini-code-assist]

Code Review

This pull request adds valuable contract tests to ensure Decimal fields are correctly serialized as strings, which is an important step to prevent precision loss in client-side applications. The new tests cover both GlobalMarketStats and AccountResponse structs. My review contains one suggestion for improving the structure of the tests to enhance clarity and maintainability.

[gemini-code-assist]

The test function is named global_market_stats_decimal_serializes_as_string, which implies its scope is limited to testing Decimal fields. The added assertion for updated_at (an i64) is outside this scope. While testing the entire contract is important, mixing concerns within a single test can make the test suite harder to understand and maintain. It's best practice for a test to have a single, clear purpose reflected in its name.

To improve clarity, I recommend moving this check to a separate test function, for example global_market_stats_numeric_fields_are_serialized_correctly. This would keep your tests focused and self-documenting.