@Test
  public void hashCodeOfDate() {
    Calendar calendar = Calendar.getInstance(TimeZone.getTimeZone("GMT"));
    calendar.setTimeInMillis(0);
    calendar.set(1970, 0, 1, 0, 0, 0);
    assertThat(Objects.hashCode(calendar.getTime())).isEqualTo(0);
    calendar.set(2020, 0, 1, 0, 0, 0);
    assertThat(Objects.hashCode(calendar.getTime())).isEqualTo(1583802735);
    calendar.set(3020, 0, 1, 0, 0, 0);
    assertThat(Objects.hashCode(calendar.getTime())).isEqualTo(-927080926);
    calendar.set(1920, 0, 1, 0, 0, 0);
    assertThat(Objects.hashCode(calendar.getTime())).isEqualTo(1670202000);
    calendar.set(1820, 0, 1, 0, 0, 0);
    assertThat(Objects.hashCode(calendar.getTime())).isEqualTo(542840753);
  }
The test serves two purposes:
<p>
Since Geode hashes rely heavily on the Java implementation hashes. If those were to differ
between version it could pose difficulties in routing or finding keys on the correct servers.
<p>
It also serves as a comparison for hashing in other languages that need to match the Java hash
algorithm for specific types.
geode-core/src/test/java/org/apache/geode/cache/util/ObjectsTest.java