DEV: Plugin-api methods for user-notifications route customizations (#24873)

spec/system/user_page/user_notifications_spec.rb

@@ -3,6 +3,7 @@
 describe "User notifications", type: :system do
   fab!(:user)
   let(:user_notifications_page) { PageObjects::Pages::UserNotifications.new }
+  let(:user_page) { PageObjects::Pages::User.new }
 
   fab!(:read_notification) { Fabricate(:notification, user: user, read: true) }
   fab!(:unread_notification) { Fabricate(:notification, user: user, read: false) }
@@ -10,7 +11,7 @@ describe "User notifications", type: :system do
   before { sign_in(user) }
 
   describe "filtering" do
-    it "saves custom picture and system assigned pictures" do
+    it "correctly filters all / read / unread notifications" do
       user_notifications_page.visit(user)
       user_notifications_page.filter_dropdown
       expect(user_notifications_page).to have_selected_filter_value("all")
@@ -28,4 +29,26 @@ describe "User notifications", type: :system do
       expect(user_notifications_page).to have_notification(unread_notification)
     end
   end
+
+  describe "setNotificationLimit & addBeforeLoadMoreNotificationsCallback plugin-api functions" do
+    it "Allows blocking loading via callback and limit" do
+      user_page.visit(user)
+
+      page.execute_script <<~JS
+        require("discourse/lib/plugin-api").withPluginApi("1.19.0", (api) => {
+          api.setNotificationsLimit(1);
+
+          api.addBeforeLoadMoreNotificationsCallback(() => {
+            return false;
+          })
+        })
+      JS
+
+      user_page.click_primary_navigation_item("notifications")
+
+      # It is 1 here because we blocked infinite scrolling. Even though the limit is 1,
+      # without the callback, we would have 2 items here as it immediately fires another request.
+      expect(user_notifications_page).to have_notification_count_of(1)
+    end
+  end
 end