# Rust Testing

> Rust Testing Best Practices

- Skill: `comeonoliver/rust-testing-2` (Agent Skill)
- Install (CLI): `npx skillmds@latest add comeonoliver/rust-testing-2`
- Raw SKILL.md: https://api.skillmd.com/api/skills/comeonoliver/rust-testing-2/raw
- Safety review: pending (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: ComeOnOliver (https://skillmd.com/u/comeonoliver)
- Updated: 2026-09-22
- Page: https://skillmd.com/skills/comeonoliver/rust-testing-2

---

# Rust Testing Best Practices

Comprehensive testing guide for Rust applications, covering CLI testing, library testing, async patterns, and CI integration. Contains 42 rules across 8 categories, prioritized by impact to guide test design, mocking strategies, and CI optimization.

## When to Apply

Reference these guidelines when:
- Writing unit tests for Rust libraries or modules
- Creating integration tests for CLI applications
- Setting up mocking with mockall or trait-based design
- Testing async code with Tokio
- Configuring CI pipelines for Rust projects

## Rule Categories by Priority

| Priority | Category | Impact | Prefix |
|----------|----------|--------|--------|
| 1 | Test Organization | CRITICAL | `org-` |
| 2 | Mocking and Test Doubles | CRITICAL | `mock-` |
| 3 | Async Testing | HIGH | `async-` |
| 4 | Property-Based Testing | HIGH | `prop-` |
| 5 | Test Fixtures and Setup | MEDIUM | `fix-` |
| 6 | Assertions and Error Testing | MEDIUM | `assert-` |
| 7 | CI Integration | MEDIUM | `ci-` |
| 8 | Test Performance | LOW-MEDIUM | `perf-` |

## Quick Reference

### 1. Test Organization (CRITICAL)

- [`org-unit-test-modules`](references/org-unit-test-modules.md) - Use cfg(test) modules for unit tests
- [`org-integration-tests-directory`](references/org-integration-tests-directory.md) - Place integration tests in tests directory
- [`org-shared-test-utilities`](references/org-shared-test-utilities.md) - Use tests/common/mod.rs for shared utilities
- [`org-binary-crate-pattern`](references/org-binary-crate-pattern.md) - Extract logic from main.rs into lib.rs
- [`org-test-naming`](references/org-test-naming.md) - Name tests after behavior not implementation
- [`org-test-cli-with-assert-cmd`](references/org-test-cli-with-assert-cmd.md) - Use assert_cmd for CLI testing

### 2. Mocking and Test Doubles (CRITICAL)

- [`mock-trait-based-design`](references/mock-trait-based-design.md) - Design for testability with traits
- [`mock-automock-attribute`](references/mock-automock-attribute.md) - Use mockall automock for complex mocking
- [`mock-avoid-mocking-owned-types`](references/mock-avoid-mocking-owned-types.md) - Avoid mocking types you own
- [`mock-expect-call-counts`](references/mock-expect-call-counts.md) - Verify mock call counts explicitly
- [`mock-predicate-arguments`](references/mock-predicate-arguments.md) - Use predicates to verify mock arguments
- [`mock-returning-sequences`](references/mock-returning-sequences.md) - Use sequences for multiple return values
- [`mock-static-methods`](references/mock-static-methods.md) - Use mock! macro for static methods

### 3. Async Testing (HIGH)

- [`async-tokio-test-macro`](references/async-tokio-test-macro.md) - Use tokio::test for async test functions
- [`async-time-control`](references/async-time-control.md) - Use paused time for timeout testing
- [`async-mock-io`](references/async-mock-io.md) - Use tokio_test for mocking async IO
- [`async-spawn-blocking`](references/async-spawn-blocking.md) - Test spawn_blocking with multi-threaded runtime
- [`async-test-channels`](references/async-test-channels.md) - Use channels for testing async communication

### 4. Property-Based Testing (HIGH)

- [`prop-proptest-basics`](references/prop-proptest-basics.md) - Use proptest for property-based testing
- [`prop-custom-strategies`](references/prop-custom-strategies.md) - Create custom strategies for domain types
- [`prop-shrinking`](references/prop-shrinking.md) - Use shrinking to find minimal failing cases
- [`prop-invariant-testing`](references/prop-invariant-testing.md) - Test invariants instead of specific values

### 5. Test Fixtures and Setup (MEDIUM)

- [`fix-rstest-fixtures`](references/fix-rstest-fixtures.md) - Use rstest fixtures for test setup
- [`fix-rstest-parametrized`](references/fix-rstest-parametrized.md) - Use rstest case for parameterized tests
- [`fix-temp-directories`](references/fix-temp-directories.md) - Use TempDir for file system tests
- [`fix-test-context`](references/fix-test-context.md) - Use test-context for setup and teardown
- [`fix-once-cell-shared-state`](references/fix-once-cell-shared-state.md) - Use OnceCell for expensive shared setup

### 6. Assertions and Error Testing (MEDIUM)

- [`assert-specific-errors`](references/assert-specific-errors.md) - Assert specific error types not just is_err
- [`assert-should-panic`](references/assert-should-panic.md) - Use should_panic for panic testing
- [`assert-debug-display`](references/assert-debug-display.md) - Implement Debug for clear failure messages
- [`assert-custom-messages`](references/assert-custom-messages.md) - Add context to assertions with custom messages
- [`assert-floating-point`](references/assert-floating-point.md) - Use approximate comparison for floating point
- [`assert-collection-contents`](references/assert-collection-contents.md) - Assert collection contents not just length

### 7. CI Integration (MEDIUM)

- [`ci-cargo-nextest`](references/ci-cargo-nextest.md) - Use cargo-nextest for faster CI
- [`ci-caching`](references/ci-caching.md) - Cache Cargo dependencies in CI
- [`ci-test-isolation`](references/ci-test-isolation.md) - Ensure test isolation in parallel CI
- [`ci-coverage`](references/ci-coverage.md) - Generate coverage reports in CI

### 8. Test Performance (LOW-MEDIUM)

- [`perf-compile-time`](references/perf-compile-time.md) - Reduce test compilation time
- [`perf-test-filtering`](references/perf-test-filtering.md) - Filter tests for faster feedback loops
- [`perf-avoid-io-in-unit-tests`](references/perf-avoid-io-in-unit-tests.md) - Avoid real IO in unit tests
- [`perf-parallel-test-execution`](references/perf-parallel-test-execution.md) - Configure parallel test threads
- [`perf-benchmark-critical-paths`](references/perf-benchmark-critical-paths.md) - Benchmark critical paths with Criterion

## How to Use

Read individual reference files for detailed explanations and code examples:

- [Section definitions](references/_sections.md) - Category structure and impact levels
- [Rule template](assets/templates/_template.md) - Template for adding new rules

## Reference Files

| File | Description |
|------|-------------|
| [references/_sections.md](references/_sections.md) | Category definitions and ordering |
| [assets/templates/_template.md](assets/templates/_template.md) | Template for new rules |
| [metadata.json](metadata.json) | Version and reference information |