Stub out requests to GOV.UK Notify, convert them into Mail::Message instances and stash them into ActionMailer::Base.deliveries

markdown_helper.rb

# app/helpers/markdown_helper.rb
require "redcarpet/render_strip"

module MarkdownHelper
  HTML_DEFAULTS = {
    escape_html: false, filter_html: false,
    hard_wrap: true, xhtml: true, safe_links_only: true,
    no_styles: true, no_images: true, no_links: false,
    with_toc_data: false, prettify: false, link_attributes: {}
  }

  PARSER_DEFAULTS = {
    no_intra_emphasis: true, tables: false, fenced_code_blocks: false,
    autolink: true, disable_indented_code_blocks: false, strikethrough: true,
    lax_spacing: false, space_after_headers: true, superscript: true,
    underline: false, highlight: false, quote: false, footnotes: false
  }

  def markdown_to_html(markup, options = {})
    markdown_parser(html_renderer(options), options).render(markup).html_safe
  end

  def markdown_to_text(markup, options = {})
    markdown_parser(text_renderer, options).render(markup).html_safe
  end

  private

  def html_renderer(options)
    Redcarpet::Render::HTML.new(options_for_renderer(options))
  end

  def text_renderer
    Redcarpet::Render::StripDown.new
  end

  def markdown_parser(renderer, options)
    Redcarpet::Markdown.new(renderer, options_for_parser(options))
  end

  def options_for_parser(options)
    PARSER_DEFAULTS.merge(options.slice(*PARSER_DEFAULTS.keys))
  end

  def options_for_renderer(options)
    HTML_DEFAULTS.merge(options.slice(*HTML_DEFAULTS.keys))
  end
end

notify.rake

# lib/tasks/notify.rake
require "notifications/client"
require "fileutils"

namespace :notify do
  task fetch_templates: :environment do
    template_dir = Rails.root.join("spec", "fixtures", "notify")
    client = Notifications::Client.new(ENV.fetch("NOTIFY_API_KEY"))
    templates = client.get_all_templates(type: "email")

    FileUtils.rm_rf template_dir
    FileUtils.mkdir_p template_dir

    templates.collection.each do |template|
      template_path = template_dir.join("#{template.id}.json")
      File.write(template_path, template.to_json)
    end
  rescue Notifications::Client::RequestError => e
    puts e.message
  end
end

notify.rb

# spec/support/notify.rb
RSpec.configure do |config|
  NOTIFY_URL = "https://api.notifications.service.gov.uk/v2/notifications/email"
  NOTIFY_APP = Module.new do
    class << self
      include MarkdownHelper

      def call(env)
        params = JSON.parse(env["rack.input"].read)
        template = templates.fetch(params["template_id"])

        message = Mail::Message.new
        subject = template["subject"].dup
        body    = template["body"].dup

        params["personalisation"].each do |key, value|
          subject.gsub!("((#{key}))", value.to_s)
          body.gsub!("((#{key}))", value.to_s)
        end

        text_part = markdown_to_text(body)
        html_part = markdown_to_html(body)

        message.message_id = "#{SecureRandom.uuid}@example.com"
        message.from = "no-reply@example.com"
        message.to = params["email_address"]
        message.subject = subject
        message.text_part = text_part
        message.html_part = html_part

        ActionMailer::Base.deliveries << message

        [ 200, { "Content-Type" => "application/json" }, ["{}"] ]
      end

      private

      def templates
        @templates ||= load_templates
      end

      def load_templates
        template_files.each_with_object({}) do |file, hash|
          hash[File.basename(file, ".json")] = JSON.parse(File.read(file))
        end
      end

      def template_files
        Dir["#{template_dir}/*.json"]
      end

      def template_dir
        Rails.root.join("spec", "fixtures", "notify")
      end
    end
  end

  config.before(:each) do |example|
    unless example.metadata[:notify] == false
      stub_request(:post, NOTIFY_URL).to_rack(NOTIFY_APP)
    end
  end
end

Actually extracted this out a bit so it could be used from Cucumber and RSpec. Also switched to using YAML for the templates so that they were more git diff friendly that one long string of JSON. You can see the final version here:

SeneddCymru/e-petitions@1256638