@Override
    public String getBucketId(IN element, BucketAssigner.Context context) {
        if (dateTimeFormatter == null) {
            dateTimeFormatter = DateTimeFormatter.ofPattern(formatString).withZone(zoneId);
        }
        return dateTimeFormatter.format(Instant.ofEpochMilli(context.currentProcessingTime()));
    }
@Test
    void testGetBucketPathWithSpecifiedFormatString() {
        DateTimeBucketAssigner bucketAssigner =
                new DateTimeBucketAssigner("yyyy-MM-dd-HH", ZoneId.of("America/Los_Angeles"));

        assertThat(bucketAssigner.getBucketId(null, mockedContext)).isEqualTo("2018-08-03-23");
    }