favgroups: make private favgroups a Gold-only option.

Make private favgroups a Gold-only option. This is for consistency with
private favorites and upvotes being Gold-only options.

Existing Members with private favgroups are allowed to keep them, as
long as they don't disable privacy. If they disable it, then they can't
re-enable it again without upgrading to Gold first.

test/functional/favorite_groups_controller_test.rb

@@ -10,7 +10,7 @@ class FavoriteGroupsControllerTest < ActionDispatch::IntegrationTest
     context "index action" do
       setup do
         @mod_favgroup = create(:favorite_group, name: "monochrome", creator: build(:moderator_user, name: "fumimi"))
-        @private_favgroup = create(:favorite_group, creator: @user, is_public: false)
+        @private_favgroup = create(:private_favorite_group)
       end
 
       should "render" do
@@ -28,7 +28,7 @@ class FavoriteGroupsControllerTest < ActionDispatch::IntegrationTest
 
       context "for private favorite groups as the creator" do
         setup do
-          CurrentUser.user = @user
+          CurrentUser.user = @private_favgroup.creator
         end
 
         should respond_to_search(is_public: "false").with { @private_favgroup }
@@ -42,13 +42,13 @@ class FavoriteGroupsControllerTest < ActionDispatch::IntegrationTest
       end
 
       should "show private favgroups to the creator" do
-        @favgroup.update!(is_public: false)
+        @favgroup.update_columns(is_public: false)
         get_auth favorite_group_path(@favgroup), @user
         assert_response :success
       end
 
       should "not show private favgroups to other users" do
-        @favgroup = create(:favorite_group, is_public: false)
+        @favgroup = create(:private_favorite_group)
         get_auth favorite_group_path(@favgroup), create(:user)
         assert_response 403
       end
@@ -91,6 +91,13 @@ class FavoriteGroupsControllerTest < ActionDispatch::IntegrationTest
         assert_response 403
         assert_not_equal("foo", @favgroup.reload.name)
       end
+
+      should "not allow non-Gold users to enable private favgroups" do
+        put_auth favorite_group_path(@favgroup), @user, params: { favorite_group: { is_private: true } }
+
+        assert_response :success
+        assert_equal(false, @favgroup.is_private?)
+      end
     end
 
     context "destroy action" do