Add end-to-end test showing Cluster health graphs

This test may take some time as we install Kubernetes, Prometheus and
wait for the "Cluster health" graphs to appear.

ee/app/views/projects/clusters/_prometheus_graphs.html.haml

 - return unless show_cluster_health_graphs?
 
-%section.settings.no-animate.expanded.cluster-health-graphs#cluster-health
+%section.settings.no-animate.expanded.cluster-health-graphs.qa-cluster-health-section#cluster-health
   %h4= s_('ClusterIntegration|Cluster health')
 
   - if @cluster&.application_prometheus_available?

qa/qa/page/project/operations/kubernetes/show.rb

@@ -21,6 +21,10 @@ module QA
               element :save_domain
             end
 
+            view 'ee/app/views/projects/clusters/_prometheus_graphs.html.haml' do
+              element :cluster_health_section
+            end
+
             def install!(application_name)
               within(".js-cluster-application-row-#{application_name}") do
                 page.has_button?('Install', wait: 30)
@@ -51,6 +55,30 @@ module QA
             def save_domain
               click_element :save_domain
             end
+
+            def wait_for_cluster_health
+              wait(max: 120, interval: 3, reload: true) do
+                has_cluster_health_graphs?
+              end
+            end
+
+            def has_cluster_health_title?
+              within_cluster_health_section do
+                has_text?('Cluster health')
+              end
+            end
+
+            def has_cluster_health_graphs?
+              within_cluster_health_section do
+                has_text?('CPU Usage')
+              end
+            end
+
+            def within_cluster_health_section
+              within_element :cluster_health_section do
+                yield
+              end
+            end
           end
         end
       end

qa/qa/specs/features/browser_ui/8_monitor/health/ee_cluster_health_spec.rb

+# frozen_string_literal: true
+
+module QA
+  context 'Monitor' do
+    describe 'Cluster health graphs', :orchestrated, :kubernetes do
+      before do
+        @cluster = Service::KubernetesCluster.new.create!
+      end
+
+      after do
+        @cluster&.remove!
+      end
+
+      it 'installs Kubernetes and Prometheus' do
+        login
+
+        create_project
+
+        create_kubernetes_cluster
+
+        verify_cluster_health_graphs
+      end
+
+      private
+
+      def login
+        Runtime::Browser.visit(:gitlab, Page::Main::Login)
+        Page::Main::Login.perform(&:sign_in_using_credentials)
+      end
+
+      def create_project
+        @project = Resource::Project.fabricate_via_api! do |p|
+          p.name = 'cluster-health'
+          p.description = 'Cluster health'
+        end
+      end
+
+      def create_kubernetes_cluster
+        Resource::KubernetesCluster.fabricate_via_browser_ui! do |c|
+          c.project = @project
+          c.cluster = @cluster
+          c.install_helm_tiller = true
+          c.install_prometheus = true
+        end
+      end
+
+      def verify_cluster_health_graphs
+        Page::Project::Operations::Kubernetes::Show.perform do |cluster|
+          cluster.refresh
+          expect(cluster).to have_cluster_health_title
+
+          cluster.wait_for_cluster_health
+        end
+      end
+    end
+  end
+end