Rubocop is a static code analyzer, and can be a wonderful tool to help you keep your style consistent either across multiple developers, or just across a project that you work on by yourself.

This will show you how you can make it part of your specs, so you don’t forget to run it, and neither does your continuous integration tool (if applicable).

Gemfile

First, add the following to your Gemfile, making sure to not require the Rubocop library by default in Rails:

group :development, :test do
  gem 'rubocop', require: false
end

Minitest

If you are using Minitest, this is where I put my test (put yours where it makes the most sense to you).

In test/linters/rubocop_test.rb:

require 'test_helper'

class RubocopTest < Minitest::Test
  def subject
    `rubocop`
  end

  def test_no_offenses_found
    assert_match(/no\ offenses\ detected/, subject)
  end
end

RSpec

If you are using RSpec, this is where I put my test (again, put yours where it makes the most sense to you).

In spec/linters/rubocop_spec.rb:

require 'spec_helper'

RSpec.describe 'rubocop analysis' do
  subject(:report) { `rubocop` }

  it 'has no offenses' do
    expect(report).to match(/no\ offenses\ detected/)
  end
end

Rubocop Settings

Now, you’ll likely notice that Rubocop can be a bit of a style… cop. To override any of the default settings, you’ll need to make sure to create a .rubocop.yml file, at the root of your project.

Minitest

To override the default Rubocop settings for Minitest, use something like the this:

In .rubocop.yml:

AllCops:
  Exclude:
    - 'Guardfile'
    - 'bin/*'
    - 'db/**/*'
    - 'config/**/*'
    - 'vendor/**/*'
    - 'test/test_helper\.rb'

Documentation:
  Enabled: false

# skips style of child classes and modules.
Style/ClassAndModuleChildren:
  Enabled: false

RSpec

To override the default Rubocop settings for RSpec, use something like the following:

AllCops:
  Exclude:
    - 'Guardfile'
    - 'bin/*'
    - 'db/**/*'
    - 'config/**/*'
    - 'vendor/**/*'
    - 'spec/rails_helper\.rb'
    - 'spec/spec_helper\.rb'

RSpec/DescribeClass:
  Exclude:
    - 'spec/features/*'
    - 'spec/views/**/*'
    - 'spec/lint/rubocop_spec\.rb'

Documentation:
  Enabled: false

# skips style of child classes and modules.
Style/ClassAndModuleChildren:
  Enabled: false

Metrics/BlockLength:
  ExcludedMethods: ['describe', 'context', 'shared_examples']