tests: add misc controller tests.

test/functional/dtext_previews_controller_test.rb

@@ -0,0 +1,12 @@
+require 'test_helper'
+
+class DtextPreviewsControllerTest < ActionController::TestCase
+  context "The dtext previews controller" do
+    context "create action" do
+      should "render" do
+        post :create, { body: "h1. Touhou\n\n* [[touhou]]" }
+        assert_response :success
+      end
+    end
+  end
+end