@Test
public void toJsonStr() {

    final Map<String, String> map = new HashMap<>();
    map.put("k1", "v1");
    map.put("k2", "v2");
    map.put("k3", "v3");
    map.put("k\"", "v\"");
    assertEquals("{\"k1\":\"v1\",\"k2\":\"v2\",\"k\\\"\":\"v\\\"\",\"k3\":\"v3\"}", Utils.toJsonStr(map));
}