fix tests

Author: liabru

src/render/Render.js

@@ -1255,6 +1255,13 @@ var Vector = require('../geometry/Vector');
      * @type render
      */
 
+    /**
+     * A reference to the `Matter.Engine` instance to be used.
+     *
+     * @property engine
+     * @type engine
+     */
+
     /**
      * A reference to the element where the canvas is to be inserted (if `render.canvas` has not been specified)
      *