@Test
public void testUtcDateTimeStringConversion() {

    ZonedDateTime now = ZonedDateTime.now();
    String expected = DateTimeFormatter.ISO_LOCAL_DATE_TIME.withZone(ZoneId.of("UTC")).format(now) + 'Z';
    String actual = DateTimeExt.toUtcDateTimeString(Instant.from(now).toEpochMilli());
    assertThat(actual).isEqualTo(expected);
}