RuboCop (Ruby)

rubocop-aaa is a custom RuboCop cop that enforces the Arrange-Act-Assert pattern in Ruby test code.

Install

# Gemfile
group :development, :test do
  gem 'rubocop-aaa', require: false
end

bundle install

Enable the cop

# .rubocop.yml
require:
  - rubocop-aaa

AAA/Pattern:
  Enabled: true
  Include:
    - 'spec/**/*.rb'
    - 'test/**/*.rb'

Cop: AAA/Pattern

Configuration

AAA/Pattern:
  TestFunctions:
    - it
    - test
    - specify
    - example
  Labels:
    arrange: [arrange]
    act:     [act]
    assert:  [assert]
  CaseSensitive: false
  AllowEmptySection: true

Examples

Given / When / Then

AAA/Pattern:
  Labels:
    arrange: [given]
    act:     [when]
    assert:  [then]

Japanese

AAA/Pattern:
  Labels:
    arrange: [準備, 前準備]
    act:     [実行]
    assert:  [検証, 確認]

What it catches

# Offense: missing "arrange"
it 'bad' do
  # act
  x = do_thing
  # assert
  expect(x).to eq(1)
end

# Offense: wrong order
it 'also bad' do
  # act
  x = do_thing
  # arrange
  y = 1
  # assert
  expect(x).to eq(y)
end

Auto-correct

When all three section comments are missing, rubocop -a (or --autocorrect) inserts a # arrange / # act / # assert template at the top of the block. You then move each comment above the code that belongs to it.

Other cases (one or two missing, wrong order, empty section) are not auto-corrected because the correct insertion point depends on the test's intent — the offense message tells you exactly what to add and where.