eslint-plugin-aaa-pattern

Enforce the Arrange-Act-Assert pattern in test code via ESLint.

Install

npm install --save-dev eslint-plugin-aaa-pattern

Usage

Flat config (ESLint v9+)

// eslint.config.js
import aaa from 'eslint-plugin-aaa-pattern'

export default [
  {
    files: ['**/*.test.{js,ts}'],
    plugins: { aaa },
    rules: {
      'aaa/pattern': 'error',
    },
  },
]

Or use the bundled recommended config:

import aaa from 'eslint-plugin-aaa-pattern'

export default [aaa.configs.recommended]

Legacy config (ESLint v8)

// .eslintrc.json
{
  "plugins": ["aaa"],
  "overrides": [
    {
      "files": ["**/*.test.js"],
      "rules": {
        "aaa/pattern": "error"
      }
    }
  ]
}

Rule: aaa/pattern

Checks that every test block contains three marker comments — arrange, act, assert — in that order.

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

  // act
  const sum = a + b

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

Options

{
  "aaa/pattern": ["error", {
    "labels": {
      "arrange": ["arrange"],
      "act":     ["act"],
      "assert":  ["assert"]
    },
    "testFunctions": ["it", "test"],
    "caseSensitive": false,
    "allowEmptySection": true
  }]
}

| Option | Default | Description | |---|---|---| | labels | { arrange: ["arrange"], act: ["act"], assert: ["assert"] } | Accepted comment text for each section. Any match in the array is accepted. | | testFunctions | ["it", "test"] | Names of test-defining calls to inspect. | | caseSensitive | false | If false, label matching ignores case. | | allowEmptySection | true | If false, report when a section has no statements between its comment and the next. |

Customizing labels

Given / When / Then

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

Japanese

Because Japanese phrasing varies (準備 vs 前準備, 検証 vs 確認), the plugin ships no Japanese preset — list the wording your team actually uses:

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

Auto-fix

When all three section comments are missing, eslint --fix (or your editor's "fix on save") inserts a // arrange / // act / // assert template at the top of the test block. You then move each comment above the code that belongs to it.

Other cases — one or two sections missing, wrong order, empty section — are reported with explicit hints in the error message but are not auto-fixed, because the correct insertion point depends on the test's intent.

License

MIT