Getting Started

aaa-lint is a family of lint plugins that enforce the Arrange-Act-Assert pattern in your test code. Every test block must contain three marker comments — arrange, act, assert — in that exact order.

it('adds two numbers', () => {
  // arrange
  const a = 1
  const b = 2

  // act
  const sum = a + b

  // assert
  expect(sum).toBe(3)
})

Why AAA?

Tests that follow the AAA pattern are easier to read and easier to modify. Reviewers can locate the setup, the action under test, and the expectations at a glance. The pattern also nudges authors to keep tests small and focused.

aaa-lint turns this convention into a mechanical check so it survives code review fatigue and onboarding turnover.

Supported languages

Language	Linter	Package
JavaScript / TypeScript	ESLint	eslint-plugin-aaa-pattern
Ruby	RuboCop	rubocop-aaa
PHP	PHP_CodeSniffer	phpcs-aaa

All three implementations share the same option surface (labels, testFunctions, caseSensitive, allowEmptySection) so projects that mix languages can keep their configuration consistent.

Customizing labels

The default labels are English — arrange, act, assert. You can override them for any language or style:

{
  "labels": {
    "arrange": ["given"],
    "act":     ["when"],
    "assert":  ["then"]
  }
}

Multiple accepted spellings per section are supported, which is handy when team members naturally write slightly different wording:

{
  "labels": {
    "arrange": ["準備", "前準備"],
    "act":     ["実行"],
    "assert":  ["検証", "確認"]
  }
}

Next steps

Pick the plugin for your stack and follow its setup guide:

• ESLint
• RuboCop
• PHP_CodeSniffer