### Question:
ConfigUtils { public static Config getDefault() { return DEFAULT_CONFIG; } private  ConfigUtils(); static Config getDefault(); static Config overlayOn(Map<String,?> overlay, Config underlying); static String getOptionalString(Config config, String key); static List<String> getOptionalStringList(Config config, String key); static Double getOptionalDouble(Config config, String key); static void set(Map<String,Object> overlay, String key, Path path); static String serialize(Config config); static Config deserialize(String serialized); static String prettyPrint(Config config); static Properties keyValueToProperties(Object... keyValues);  }### Answer:
@Test public void testDefaultConfig() { Config config = ConfigUtils.getDefault(); assertEquals("yarn", config.getString("oryx.batch.streaming.master")); }