Testing in Rust

Last reviewed May 28, 2026 Content v20260528

Track mode: server_compiled
Means: Compiled runner
Reading: ~1 min
Level: advanced

This lesson

This lesson teaches Testing in Rust: the syntax, APIs, and habits you need before advancing in Rust.

Teams ship Testing in Rust on every Rust codebase—skipping it leaves gaps in debugging and code reviews.

You will apply Testing in Rust in contexts like: Infrastructure CLIs, proxies, game engines, blockchain nodes, and latency-sensitive backends.

Write Rust with fn main(), click Run on server—the dev runner compiles main.rs with rustc and runs the binary; fix borrow errors from stderr (requires Rust toolchain; LEARNING_RUNNER_ENABLED=true).

When functions, arrays, and basic OOP from intermediate lessons are familiar.

Unit tests live in the same file with #[cfg(test)] mod tests; integration tests go in tests/. Run with cargo test locally—playground simulates assertions with assert!.

assert macros

assert_eq!(add(2, 2), 4);
assert!(score > 0);

Self-check

Which macro compares equality in tests?
Where do integration tests live in Cargo projects?

Test organization

Unit tests compile only in test configuration—zero cost in release binaries. Integration tests in tests/*.rs see only the public API, mirroring how external users call your crate.

Use #[should_panic] for expected failures and Result tests with ? inside test functions.

Interview tip Lesson completion confidence

Can you explain this lesson in 30 seconds without reading notes?

Self-reflection (saved on this device)

Not saved yet.

Playground

Runs on the configured server runner (dev: npm run runner with LEARNING_RUNNER_ENABLED=true). Output appears below the editor.

Code runner not available

Server runner is disabled. Set LEARNING_RUNNER_ENABLED=true and LEARNING_RUNNER_URL in .env (see .env.example).

Check yourself

Multiple choice — immediate feedback.

Discussion

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Starter discussion topics

#[test] attribute?
#[should_panic]?

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