final RenderData renderData = new RenderData();
        method.invoke(action, renderData);

        @SuppressWarnings("unchecked")
        final List<String> extraFieldNames = (List<String>) renderData.getDataMap().get("extraFieldNames");
        assertNotNull(extraFieldNames);
        // Config-defined field "anchor" is not in STANDARD_EDIT_FIELDS, so it appears as extra
        assertTrue(extraFieldNames.contains("anchor"));