tests: add note previews controller tests.

test/functional/note_previews_controller_test.rb

@@ -0,0 +1,12 @@
+require 'test_helper'
+
+class NotePreviewsControllerTest < ActionController::TestCase
+  context "The note previews controller" do
+    context "show action" do
+      should "work" do
+        get :show, { body: "<b>test</b>", format: "json" }
+        assert_response :success
+      end
+    end
+  end
+end