@Test void getDays_doesntLookEarlierThan1970() {
    assertThat(DateUtil.epochDays(DAYS.toMillis(2), DAYS.toMillis(3)))
        .containsExactly(0L, DAYS.toMillis(1), DAYS.toMillis(2));
  }
Looking back earlier than 1970 is likely a bug
zipkin/src/test/java/zipkin2/internal/DateUtilTest.java