testing database queries in rails

describe 'database performance' do
  before  { @sql_calls = 0 }
  after   { ActiveSupport::Notifications.unsubscribe(@subscription) }

  it 'makes a minimum of db queries' do
    @subscription = ActiveSupport::Notifications.subscribe('sql.active_record') do |event|
      @sql_calls += 1
    end

    get :index, attributes.merge(format: :json)
    expect(@sql_calls).to be < 25
  end
end