Rust testing patterns including unit tests, integration tests, async testing, property-based testing, mocking, and coverage. Follows TDD methodology. Use when writing Rust tests — unit, integration, async, property-based, or coverage.

Rust Testing Patterns Comprehensive Rust testing patterns for writing reliable, maintainable tests following TDD methodology. When to Use Writing new Rust functions, methods, or traits Adding test coverage to existing code Creating benchmarks for performance critical code Implementing property based tests for input validation Following TDD workflow in Rust projects How It Works 1. Identify target code — Find the function, trait, or module to test 2. Write a test — Use [test] in a [cfg(test)] module, rstest for parameterized tests, or proptest for property based tests 3. Mock dependencies — Use mockall to isolate the unit under test 4. Run tests (RED) — Verify the test fails with the expected error 5. Implement (GREEN) — Write minimal code to pass 6. Refactor — Improve while keeping tests green 7. Check coverage — Use cargo llvm cov, target 80%+ TDD Workflow for Rust The RED GREEN REFACTOR Cycle Step by Step TDD in Rust Unit Tests Module Level Test Organization Assertion Macros Error and Panic Testing Testing Result Returns Testing Panics Integration Tests File Structure Writing Integration Tests Async Tests With Tokio Test Organization Patterns Parameterized Tests with rstest Test Helpers Property Based Testing with proptest Basic Property Tests Custom Strategies Mocking with mockall Trait Based Mocking Doc Tests Executable Documentation /// use my crate::add; /// /// assert eq!(add(2, 3), 5); /// assert eq!(add( 1, 1), 0); /// no run /// use my crate::parse config; /// /// let config = parse config(r "port = 8080" ).unwrap(); /// assert eq!(config.port, 8080); /// no run /// use my crate::parse config; /// /// assert!(parse config("}{invalid").is err()); /// Benchmarking with Criterion Test Coverage Running Coverage Coverage Targets Code Type Target Critical business logic 100% Public API 90%+ General code 80%+ Generated / FFI bindings Exclude Testing Commands Best Practices DO: Write tests FIRST (TDD) Use [cfg(test)] modules for unit tests Test behavior, not implementation Use descriptive test names that explain the scenario Prefer assert eq! over assert! for better error messages Use ? in tests that return Result for cleaner error output Keep tests independent — no shared mutable state DON'T: Use [should panic] when you can test Result::is err() instead Mock everything — prefer integration tests when feasible Ignore flaky tests — fix or quarantine them Use sleep() in tests — use channels, barriers, or tokio::time::pause() Skip error path testing CI Integration Remember : Tests are documentation. They show how your code is meant to be used. Write them clearly and keep them up to date.

rust-testing