Capybara Visual Regression Helper

screenshot.rb

module Support
  module ScreenshotHelper
    def ensure_pixel_perfection
      PixelPerfect.new(page)
    end

    class PixelPerfect
      attr_reader :page
      def initialize(page)
        @page = page
      end

      def of(name)
        @name = name.parameterize
        self
      end

      def using(selector)
        @selector = selector
        self
      end

      def retina
        @retina = true
        self
      end

      def call
        raise ArgumentError unless @name && @selector

        image = screenshot_element

        if existing_image_path.exist?
          diff_image, pixels_changed = existing_image.compare_channel(image, Magick::AbsoluteErrorMetric)
          percent_change = pixels_changed / (existing_image.rows * existing_image.columns) * 100

          if pixels_changed > 0
            diff_image.write(diff_path)
            raise "ScreenshotHelper: `#{@selector}` had %#{percent_change.round(2)} pixel change. A diff has been saved to #{diff_path}"
          end
        else
          FileUtils.copy(image_path, existing_image_path)
        end
      ensure
        image_path.delete
      end

      private

      def image_path
        Rails.root.join("tmp", "#{@name}.png")
      end

      def diff_path
        Rails.root.join("tmp", "diff-#{@name}.png")
      end

      def existing_image_path
        Rails.root.join("regression_specs", "fixtures", "#{@name}.png")
      end

      def existing_image
        Magick::Image.read(existing_image_path)[0]
      end

      def screenshot_element(padding: 25)
        el_count = page.all(@selector).count
        raise "ScreenshotHelper: #{count} elements found on the page for `#{@selector}`" unless el_count == 1

        el = page.find(@selector)
        location = el.native.location
        size = el.native.size

        if @retina
          location.x *= 2
          location.y *= 2
          size.width *= 2
          size.height *= 2
          padding *= 2
        end

        image = page.save_screenshot(image_path)
        cropped_image = Magick::Image.read(image)[0].crop(location.x - padding/2, location.y - padding/2, size.width + padding, size.height + padding)
        cropped_image.write(image)

        cropped_image
      end
    end
  end
end

Should line 68 be interpolating el_count as opposed to count?

Also I had to edit line 45 to be image_path.delete if File.file?(image_path). I had a new image that didn't have a screenshot saved and matched 2 elements in the dom. So it was triggering the raise on line 68, but I wasn't actually seeing that error message because it was failing again in the ensure since didn't exist to delete.

Errno::ENOENT: No such file or directory @ dir_s_rmdir - /Users/brian/src/project/tmp/person-row.png

You are right @l3rl4n