Rust Testing

What it does

This skill assists with writing high-quality tests for Rust code, particularly within the context of developing backend services and APIs using the codex-rs framework. It provides guidance on test architecture, assertions, mock servers, test data generation, event-driven testing, ensuring determinism, snapshot testing, and integration test infrastructure. The skill encodes best practices established by top codex-rs contributors to ensure consistent and effective Rust testing workflows.

When to use it

• Writing new tests for any Rust module in codex-rs.
• Adding regression tests when fixing bugs (typically 3-6 tests per pull request).
• Creating integration tests that interact with the Responses API using SSE mocks.
• Modifying TUI rendering code requiring snapshot coverage.
• Reviewing existing test code for adherence to established codebase conventions.

Key capabilities

• Guidance on test architecture (file organization, imports, isolation)
• Best practices for assertions, including pretty_assertions and whole-object comparison.
• Mock server implementation using wiremock and SSE builders.
• Test data generation with typed construction and BTreeMap.
• Event testing patterns involving submit/wait cycles and predicate matching.
• Techniques for ensuring determinism, such as stable IDs and environment isolation.
• Snapshot testing workflows utilizing the insta framework.
• Integration test infrastructure compatible with Bazel.

Example prompts

• "Show me how to structure a new Rust test file."
• "How do I mock an SSE response for integration testing?"
• "What's the best way to write assertions in my Rust tests?"

Tips & gotchas

• Start by focusing on the "CRITICAL" rules (Test Architecture and Assertions) as they apply to all tests.
• When writing integration tests with API mocks, prioritize the "HIGH" rules related to mock servers and test data.
• The skill references several files for detailed guidance; consult references/_sections.md for an overview of rule categories and impact levels.