### Question:
WallclockTimestampExtractor implements TimestampExtractor { @Override public long extract(final ConsumerRecord<Object, Object> record, final long previousTimestamp) { return System.currentTimeMillis(); }  @Override long extract(final ConsumerRecord<Object, Object> record, final long previousTimestamp);  }### Answer:
@Test public void extractSystemTimestamp() { final TimestampExtractor extractor = new WallclockTimestampExtractor(); final long before = System.currentTimeMillis(); final long timestamp = extractor.extract(new ConsumerRecord<>("anyTopic", 0, 0, null, null), 42); final long after = System.currentTimeMillis(); assertThat(timestamp, is(new InBetween(before, after))); }