Support non-rails applications with minitest

[pftg]

To setup non-rails app I need at least to provide such code:

module Rails
  def self.root
    File.expand_path("../../", __FILE__)
  end

  def self.application
    Capybara.app
  end
end

class ApplicationSystemTestCase < Minitest::Test
  include Capybara::DSL
  include Capybara::Minitest::Assertions
  include CapybaraScreenshotDiff::DSL

  def screenshot(*, **)
    super
  rescue CapybaraScreenshotDiff::ExpectationNotMet => e
    raise ::Minitest::Assertion, e.message
  end

  alias_method :assert_matches_screenshot, :screenshot

  def setup
    super
    if ::Capybara::Screenshot.window_size
      ::Capybara::Screenshot::BrowserHelpers.resize_to(::Capybara::Screenshot.window_size)
    end
  end

  def teardown
    super
    Capybara.reset_sessions!

    errors = verify_screenshots!(@test_screenshots)
    failures << ::Minitest::Assertion.new(errors.join("\n\n")) if errors && !errors.empty?
  end
end