Fix Sidekiq health banner overlap (#3432)

test/system/sidekiq_health_banner_test.rb

@@ -0,0 +1,26 @@
+require "application_system_test_case"
+
+class SidekiqHealthBannerTest < ApplicationSystemTestCase
+  setup do
+    @health = Object.new
+    @health.stubs(:healthy?).returns(false)
+    @health.stubs(:reason).returns(:queue_backed_up)
+
+    Rails.application.config.stubs(:app_mode).returns("self_hosted".inquiry)
+    Redis.any_instance.stubs(:ping).returns("PONG")
+    SidekiqHealth.stubs(:current).returns(@health)
+  end
+
+  test "dashboard data warning reserves space instead of overlapping the page header" do
+    sign_in users(:sure_support_staff)
+    visit root_path
+
+    assert_selector "[data-testid='sidekiq-health-banner']"
+
+    banner_rect = page.evaluate_script("document.querySelector('[data-testid=\"sidekiq-health-banner\"]').getBoundingClientRect()")
+    heading_rect = page.evaluate_script("document.querySelector('h1').getBoundingClientRect()")
+
+    assert_operator banner_rect["bottom"], :<=, heading_rect["top"],
+      "expected the stale-data warning to finish above the dashboard heading"
+  end
+end