show_screenshot helper for PhantomJS tests.

.gitignore

public/screenshot-*.png

example_spec.rb

describe "Things" do
  it "does stuff", :js do
    visit my_path
    show_screenshot  # Writes screenshot-4.png, for line 4.
    show_screenshot :my_name  # Writes screenshot-my_name.png
  end
end

feature_helpers.rb

module FeatureHelpers
  def show_screenshot(given_suffix = :default_suffix)
    if given_suffix == :default_suffix
      # The line may be e.g. "/dir/my_spec.rb:123:in …"
      called_from_line = caller.first[/.*?:(\d+):/, 1]

      suffix = "line-#{called_from_line}"
    else
      suffix = given_suffix
    end

    file_name = "screenshot-#{suffix}.png"
    url = "http://our-app.dev/#{file_name}"

    # https://github.com/teampoltergeist/poltergeist#taking-screenshots-with-some-extensions
    save_screenshot(Rails.root.join("public/#{file_name}"), full: true)

    # https://github.com/busyloop/lolcat - Colorizes the output, in our case like a rainbow.
    Lol.println("Screenshot can be found at: #{url}", os: 10, freq: 0.1, spread: 1)
  end
end

RSpec.configure do |config|
  config.include FeatureHelpers, type: :feature
end

We write to public and output a URL since we develop inside a VM. If you develop on OS X straight on the host machine, you could e.g. write to /tmp and even open /tmp/file.png to auto-open it.