Set browser screen size in rspec + capybara suite for responsive web design test.

screen_size.rb

# spec/support/screen_size.rb

module ScreenSize

  SCREENS = {
    small:  { width: 590 , height: 768 },
    medium: { width: 1025, height: 768 },
    large:  { width: 1280, height: 768 }
  }

  def default_size
    "large"
  end

  def set_screen_size(size)
    screen_size = SCREENS[size.to_sym]
    raise "Invalid screen size #{size}. It should be :small, :medium or :large" if screen_size.blank?
    Capybara.current_session.driver.browser.manage.window.resize_to(screen_size[:width], screen_size[:height]) if Capybara.current_session.driver.browser.respond_to? 'manage'
  end
end