AO3-5259 Deduplicate and order admin post tags

app/controllers/admin_posts_controller.rb

@@ -14,7 +14,7 @@ def index
     @admin_posts ||= AdminPost
     if params[:language_id].present? && (@language = Language.find_by(short: params[:language_id]))
       @admin_posts = @admin_posts.where(language_id: @language.id)
-      @tags = AdminPostTag.joins(:admin_posts).where(admin_posts: { language_id: @language.id })
+      @tags = AdminPostTag.distinct.joins(:admin_posts).where(admin_posts: { language_id: @language.id }).order(:name)
     else
       @admin_posts = @admin_posts.non_translated
       @tags = AdminPostTag.order(:name)

spec/controllers/admin_posts_controller_spec.rb

@@ -4,6 +4,22 @@
   include LoginMacros
   include RedirectExpectationHelper
 
+  describe "GET #index" do
+    context "when filtering by language" do
+      let(:translated_post1) { create(:admin_post, tag_list: "xylophone,aardvark") }
+      let!(:translation_post1) { create(:admin_post, translated_post_id: translated_post1.id, language: create(:language, short: "fr")) }
+      let(:translated_post2) { create(:admin_post, tag_list: "xylophone,aardvark") }
+      let!(:translation_post2) { create(:admin_post, translated_post_id: translated_post2.id, language: translation_post1.language) }
+      let!(:untranslated_post) { create(:admin_post, tag_list: "uncommon tag")}
+
+      it "assigns the admin post tags for the language ordered by name" do
+        get :index, params: { language_id: "fr" }
+
+        expect(assigns[:tags].map(&:name).join(", ")).to eql("aardvark, xylophone")
+      end
+    end
+  end
+
   describe "POST #create" do
     before { fake_login_admin(create(:admin, roles: ["communications"])) }