rust-tests-guidelines

Organize Rust tests in #[cfg(test)] modules within source files or in a tests/ directory at your crate root. Run all tests with cargo test, which discovers and executes unit, integration, and property-based tests automatically.

Unit tests validate individual components and live in #[cfg(test)] modules alongside source code. Integration tests verify interactions between modules and crates; place them in the tests/ directory where cargo test runs them as separate binaries.

Property-based testing explores edge cases and invariants by generating random inputs. Use proptest to define properties your code must hold across many test cases, catching bugs unit tests might miss through exhaustive input variation.

Snapshot testing captures outputs and compares future runs against stored snapshots to detect regressions. Insta provides a Rust snapshot testing library that stores snapshots inline or as separate files, ideal for validating complex outputs remain stable.

Yes. Rust projects scale across all three testing types: use unit tests for isolated logic, integration tests for cross-module behavior, and property-based tests with proptest to verify invariants. Run all with cargo test.

Place unit tests in #[cfg(test)] modules within each crate's library code. Use the tests/ directory in each crate for integration tests. This structure keeps tests close to implementation while enabling end-to-end validation across crate boundaries.