RuboCop configuration which has the same code style checking as official Ruby on Rails.

Official RoR RuboCop Configuration

Add this line to your application's Gemfile:

gem "rubocop-rails_config"

Add this line to your application's .rubocop.yml:

inherit_gem:
  rubocop-rails_config:
    - config/rails.yml

Or just run:

$ rails generate rubocop_rails_config:install

If you'd like to change TargetRubyVersion, see Customization.

assert_not and assert_not_xxx methods are Rails assertion extension, so if you want to use these methods, require activesupport gem and inherit ActiveSupport::TestCase.

class AssertNotTest < ActiveSupport::TestCase
  def test_assert_not_method
    assert_not ...(code)...
  end

  def test_assert_not_nil_method
    assert_not_nil ...(code)...
  end
end

See also. ActiveSupport::Testing::Assertions

If you'd like to customize the rubocop setting on your project, you can override it.

For example, if you want to change TargetRubyVersion, you can do it like:

# .rubocop.yml
inherit_gem:
  rubocop-rails_config:
    - config/rails.yml

# Override Setting
AllCops:
  TargetRubyVersion: 3.0

This overrides config/rails.yml setting with TargetRubyVersion: 3.0.

The gem is available as open source under the terms of the MIT License.