quality-unit-testing

Quality Unit Testing for Rust

Write tests that catch real bugs and provide deployment confidence.

Core Principles

Quality over coverage: Tests should catch real bugs, not just boost percentages.

Quick Reference

Naming: test_<function><scenario><expected>

#[test] fn test_process_payment_insufficient_funds_returns_error()

#[tokio::test] async fn test_withdraw_valid_amount_decreases_balance()

AAA Pattern (Arrange-Act-Assert)

#[test] fn test_account_withdraw_decreases_balance() { // Arrange let mut account = Account::new(100);

// Act
let result = account.withdraw(30);

// Assert
assert!(result.is_ok());
assert_eq!(account.balance(), 70);

}

Isolation

✓ Mock: APIs, databases, file systems, external services ✗ Don't mock: Value types, pure functions, code under test

Single Responsibility

Each test verifies ONE behavior with ONE reason to fail.

Rust-Specific Patterns

// Async tests #[tokio::test] async fn test_async_operation() { /* ... */ }

// Result-based tests #[test] fn test_operation() -> anyhow::Result<()> { /* ... */ }

// Test builders let episode = TestEpisodeBuilder::new() .with_task("Test task") .completed(true) .build();

// RAII cleanup struct TestDb(TempDir); impl Drop for TestDb { fn drop(&mut self) { /* auto cleanup */ } }

Success Metrics

✓ Deploy without manual testing ✓ Test failures pinpoint exact problems ✓ Refactoring doesn't break unrelated tests ✓ Tests run in milliseconds

Workflow

Creating Tests:

Reviewing Tests:

Source Transparency