Fix exception in /pools/:id/order/edit.

test/functional/pool_orders_controller_test.rb

@@ -0,0 +1,21 @@
+require 'test_helper'
+
+class PoolOrdersControllerTest < ActionDispatch::IntegrationTest
+  context "The pool orders controller" do
+    context "edit action" do
+      should "render" do
+        user = create(:user)
+
+        as(user) do
+          posts = create_list(:post, 3)
+          pool = create(:pool)
+          posts.each { |p| pool.add!(p) }
+
+          get_auth edit_pool_order_path(pool), user
+          assert_response :success
+          assert_select "article.post-preview", 3
+        end
+      end
+    end
+  end
+end