Serving configs: Add Finder Frontend preview

This allows users to preview the results from a serving config on Finder
Frontend using the `debug_serving_config` parameter.

app/models/serving_config.rb

@@ -26,4 +26,12 @@ class ServingConfig < ApplicationRecord
 
   validates :display_name, presence: true
   validates :remote_resource_id, presence: true, uniqueness: true
+
+  # A URL to preview this serving config on Finder Frontend
+  def preview_url
+    FinderFrontendSearch.new(
+      keywords: "example search",
+      debug_serving_config: remote_resource_id,
+    ).url
+  end
 end

app/views/serving_configs/show.html.erb

@@ -16,6 +16,16 @@
   title: @serving_config.display_name,
 } %>
 
+<div class="actions">
+  <%= render "govuk_publishing_components/components/button", {
+    text: t(".buttons.preview"),
+    href: @serving_config.preview_url,
+    target: "_blank",
+    secondary_quiet: true,
+    inline_layout: true
+  } %>
+</div>
+
 <%= render "govuk_publishing_components/components/summary_list", {
   items: [
     {

config/locales/en.yml

@@ -170,3 +170,6 @@ en:
   serving_configs:
     index:
       page_title: Serving configs
+    show:
+      buttons:
+        preview: Preview on GOV.UK

spec/models/serving_config_spec.rb

@@ -48,4 +48,22 @@
       )
     end
   end
+
+  describe "#preview_url" do
+    subject(:serving_config) { create(:serving_config, remote_resource_id: "hello") }
+
+    let(:finder_frontend_search) do
+      instance_double(FinderFrontendSearch, url: "https://example.org")
+    end
+
+    before do
+      allow(FinderFrontendSearch).to receive(:new)
+        .with(keywords: "example search", debug_serving_config: "hello")
+        .and_return(finder_frontend_search)
+    end
+
+    it "returns the preview URL" do
+      expect(serving_config.preview_url).to eq("https://example.org")
+    end
+  end
 end