rust-testing

Place a #[cfg(test)] module with #[test] functions in the same file as your code, using use super::* to access private items. Run them with cargo test, and prefer assert_eq! over assert! for clearer failure messages.

Use the #[tokio::test] attribute instead of #[test] to run async test functions. You can test timeouts by wrapping operations in tokio::time::timeout and asserting the result is an error.

rstest provides parameterized tests and fixtures for known input cases, while proptest generates random inputs to verify properties like roundtrip encoding or sort invariants. Use rstest for concrete scenarios and proptest for edge-case discovery.

Use the mockall crate with #[automock] on your trait to generate a mock implementation. Configure expectations with methods like expect_find_by_id().with(eq(42)).times(1).returning(...) to control behavior and verify call counts.

Install cargo-llvm-cov and run cargo llvm-cov for a summary, --html for a report, or --fail-under-lines 80 to enforce a threshold in CI. Target 100% for critical logic, 90%+ for public APIs, and 80%+ for general code.

Avoid #[should_panic] when the function returns a Result, since testing Result::is_err() gives more precise assertions on specific error variants. Reserve should_panic for genuine panic conditions, ideally with an expected message.