Add transient spec for discussion comments

qa/qa/specs/features/browser_ui/2_plan/transient/comment_on_discussion_spec.rb

+# frozen_string_literal: true
+
+module QA
+  RSpec.describe 'Plan', :transient do
+    describe 'Discussion comments transient bugs' do
+      let(:user1) do
+        Resource::User.fabricate_or_use(Runtime::Env.gitlab_qa_username_1, Runtime::Env.gitlab_qa_password_1)
+      end
+
+      let(:my_first_reply) { 'This is my first reply' }
+      let(:my_second_reply) { "@#{Runtime::Env.gitlab_qa_username_1}" }
+      let(:my_third_reply) { "@#{Runtime::Env.gitlab_qa_username_1} This is my third reply" }
+      let(:my_fourth_reply) { '/close' }
+
+      before do
+        Flow::Login.sign_in
+      end
+
+      it 'comments with mention on a discussion in an issue', testcase: 'https://gitlab.com/gitlab-org/quality/testcases/-/issues/1753' do
+        Runtime::Env.transient_trials.times do |i|
+          QA::Runtime::Logger.info("Transient bug test action - Trial #{i}")
+
+          Resource::Issue.fabricate_via_api!.visit!
+
+          Page::Project::Issue::Show.perform do |issue_page|
+            issue_page.select_all_activities_filter
+            issue_page.start_discussion('My first discussion')
+            issue_page.reply_to_discussion(1, my_first_reply)
+
+            expect(issue_page).to have_comment(my_first_reply)
+
+            issue_page.reply_to_discussion(1, my_second_reply)
+
+            expect(issue_page).to have_comment(my_second_reply)
+
+            issue_page.reply_to_discussion(1, my_third_reply)
+
+            expect(issue_page).to have_comment(my_third_reply)
+
+            issue_page.reply_to_discussion(1, my_fourth_reply)
+
+            expect(issue_page).to have_system_note('closed')
+          end
+        end
+      end
+    end
+  end
+end