@Test
    public void numberOfDaysSinceEpoch() {
        final long now = System.currentTimeMillis();
        final long days = DateUtils.numberOfDaysSinceEpoch(now);
        final int oneDayMilli = 24*60*60*1000;
        assertTrue(now > days*oneDayMilli);
        assertTrue((now - days*oneDayMilli) <= oneDayMilli);
    }
Tests the Date marshalling and unmarshalling. Asserts that the value is
same before and after marshalling/unmarshalling
aws-java-sdk-core/src/test/java/com/amazonaws/util/DateUtilsTest.java