Pattern 1: AAA Pattern

Context

You are writing or reviewing a test in Chicago TDD Tools. You want the test to communicate intent instantly and fail with a precise message when behavior regresses.

Problem

Tests that intermingle setup, behavior, and assertions become hard to scan. When the failure occurs, teammates must untangle implicit state, which slows feedback and hides missing assertions.

Solution

Structure every test body into three explicit phases – Arrange, Act, Assert – and let the framework enforce it. Use the test!, async_test!, or fixture_test! macros so that comments and code read in a top-to-bottom narrative.

Forces

• Readability vs. flexibility: expressive labels without duplicating boilerplate
• Fast diagnosis vs. runtime overhead: compile-time enforcement should cost nothing
• Behavior proof vs. implementation detail: assertions must verify observable outcomes

Examples

#![allow(unused)]
fn main() {
use chicago_tdd_tools::prelude::*;

test!(test_scaling_multiplier, {
    // Arrange
    let multiplier = 3;
    let input = 7;

    // Act
    let result = multiplier * input;

    // Assert
    assert_eq!(result, 21, "multiplier should scale the input");
});
}

Async tests follow the same skeleton:

#![allow(unused)]
fn main() {
use chicago_tdd_tools::prelude::*;

async_test!(test_fetch_customer, {
    // Arrange
    let client = FakeCrmClient::connected();

    // Act
    let customer = client.fetch("cust-123").await?;

    // Assert
    assert_eq!(customer.id, "cust-123");
    Ok(())
});
}

Related Patterns

• Pattern 2: Error Path Testing
• Pattern 5: Real Collaborators
• Pattern 11: Zero-Cost Abstractions