FIX: more precise unread message detection (#20588)

plugins/chat/spec/system/mark_message_as_read.rb

@@ -0,0 +1,48 @@
+# frozen_string_literal: true
+
+RSpec.describe "Mark message as read", type: :system, js: true do
+  fab!(:current_user) { Fabricate(:user) }
+  fab!(:channel_1) { Fabricate(:chat_channel) }
+
+  let(:chat_page) { PageObjects::Pages::Chat.new }
+  let(:channel_page) { PageObjects::Pages::ChatChannel.new }
+  let(:membership) { Chat::ChatChannelMembershipManager.new(channel_1).find_for_user(current_user) }
+
+  before do
+    chat_system_bootstrap
+    channel_1.add(current_user)
+    membership.update!(last_read_message_id: first_unread.id)
+    25.times { |i| Fabricate(:chat_message, chat_channel: channel_1) }
+  end
+
+  context "when the full message is not visible" do
+    fab!(:first_unread) { Fabricate(:chat_message, chat_channel: channel_1) }
+
+    it "doesn’t mark it as read" do
+      sign_in(current_user)
+      before_last_message = Fabricate(:chat_message, chat_channel: channel_1)
+      last_message = Fabricate(:chat_message, chat_channel: channel_1)
+      chat_page.visit_channel(channel_1)
+
+      page.execute_script("document.querySelector('.chat-messages-scroll').scrollTo(0, -5)")
+
+      try_until_success(timeout: 5) do
+        membership.reload.last_read_message_id = before_last_message.id
+      end
+    end
+  end
+
+  context "when the full message is visible" do
+    fab!(:first_unread) { Fabricate(:chat_message, chat_channel: channel_1) }
+
+    it "marks it as read" do
+      sign_in(current_user)
+      last_message = Fabricate(:chat_message, chat_channel: channel_1)
+      chat_page.visit_channel(channel_1)
+
+      page.execute_script("document.querySelector('.chat-messages-scroll').scrollTo(0, 0)")
+
+      try_until_success(timeout: 5) { membership.reload.last_read_message_id = last_message.id }
+    end
+  end
+end