@Test
    void testEquality() {
        assertEquals(new HashMap(0).hashCode(), Map.of().hashCode());
        assertEquals(new HashMap(0), Map.of());
    }
Aggregate metrics are not cloned into new snapshot. In turn, a metric
set with only aggregates will be added as an empty set if we do not
filter these away at clone time. This test ensures that we do just that.
If/when we start carrying aggregates across snapshots, this test will
most likely be deprecated.
container-core/src/test/java/com/yahoo/container/jdisc/state/MetricSnapshotTest.java