Simplecov for Rails Engine with Minitest

simplecov_rails_engine_minitest.rb

# add this to your main library file
# lib/<engine_name>.rb
if ENV['RAILS_ENV'] == 'test'
  require 'simplecov'

  SimpleCov.start do
    load_profile "test_frameworks"

    add_filter %r{^/config/}
    add_filter %r{^/db/}

    add_group "Controllers", "app/controllers"
    add_group "Channels", "app/channels"
    add_group "Models", "app/models"
    add_group "Mailers", "app/mailers"
    add_group "Helpers", "app/helpers"
    add_group "Jobs", %w[app/jobs app/workers]
    add_group "DynamicLinks", "lib/"
  end
end

# reference https://github.com/simplecov-ruby/simplecov/issues/434#issuecomment-228210164