Fix issue and add tests that prevent something like this. (#2320)

lib/screens/v2/candidate_generator/elevator.ex

@@ -32,8 +32,8 @@ defmodule Screens.V2.CandidateGenerator.Elevator do
         evergreen_content_instances_fn \\ &Evergreen.evergreen_content_instances/2
       ) do
     Enum.concat([
-      header_instance(config, now),
-      footer_instance(config),
+      [header_instance(config, now)],
+      [footer_instance(config)],
       elevator_closure_instances_fn.(config),
       evergreen_content_instances_fn.(config, now)
     ])

test/screens/v2/candidate_generator/elevator_test.exs

@@ -3,6 +3,7 @@ defmodule Screens.V2.CandidateGenerator.ElevatorTest do
 
   alias ScreensConfig.{Screen, V2}
   alias Screens.V2.CandidateGenerator.Elevator
+  alias Screens.V2.WidgetInstance.{Footer, NormalHeader}
 
   setup do
     config = %Screen{
@@ -26,4 +27,32 @@ defmodule Screens.V2.CandidateGenerator.ElevatorTest do
               }} == Elevator.screen_template()
     end
   end
+
+  describe "candidate_instances/4" do
+    test "returns expected header and footer", %{config: config} do
+      now = ~U[2020-04-06T10:00:00Z]
+      elevator_closure_instances_fn = fn _ -> [] end
+      evergreen_content_instances_fn = fn _, _ -> [] end
+
+      expected_header = %NormalHeader{
+        screen: config,
+        icon: nil,
+        text: "Elevator 1",
+        time: now
+      }
+
+      expected_footer = %Footer{screen: config}
+
+      actual_instances =
+        Elevator.candidate_instances(
+          config,
+          now,
+          elevator_closure_instances_fn,
+          evergreen_content_instances_fn
+        )
+
+      assert expected_header in actual_instances
+      assert expected_footer in actual_instances
+    end
+  end
 end