public Collection<ResultPartitionID> getTrackedPartitions(K key) {
        Preconditions.checkNotNull(key);
        return trackedPartitionsPerKey.getOrDefault(key, Collections.emptySet());
    }
@Test
    void testGetTrackedPartitions() {
        final PartitionTable<JobID> table = new PartitionTable<>();

        table.startTrackingPartitions(JOB_ID, Collections.singletonList(PARTITION_ID));

        assertThat(table.getTrackedPartitions(JOB_ID)).containsExactly(PARTITION_ID);
    }