static String currentTimestamp(Clock clock) {
        SimpleDateFormat df = new SimpleDateFormat("yyyyMMdd'T'HHmmss'Z'");
        df.setTimeZone(TimeZone.getTimeZone("UTC"));
        return df.format(Instant.now(clock).toEpochMilli());
    }
@Test
    public void currentTimestamp() {
        // given
        Clock clock = Clock.fixed(Instant.ofEpochMilli(1585909518929L), ZoneId.systemDefault());

        // when
        String currentTimestamp = AwsRequestUtils.currentTimestamp(clock);

        // then
        assertEquals("20200403T102518Z", currentTimestamp);
    }