### Question:
SCMNodeStorageStatMap implements SCMNodeStorageStatMXBean { public boolean isKnownDatanode(UUID datanodeID) { Preconditions.checkNotNull(datanodeID); return scmNodeStorageReportMap.containsKey(datanodeID); } SCMNodeStorageStatMap(OzoneConfiguration conf); boolean isKnownDatanode(UUID datanodeID); List<UUID> getDatanodeList(
      UtilizationThreshold threshold); void insertNewDatanode(UUID datanodeID,
      Set<StorageLocationReport> report); void updateDatanodeMap(UUID datanodeID,
      Set<StorageLocationReport> report); StorageReportResult processNodeReport(UUID datanodeID,
      StorageContainerDatanodeProtocolProtos.NodeReportProto nodeReport); @Override long getCapacity(UUID dnId); @Override long getRemainingSpace(UUID dnId); @Override long getUsedSpace(UUID dnId); @Override long getTotalCapacity(); @Override long getTotalSpaceUsed(); @Override long getTotalFreeSpace(); void removeDatanode(UUID datanodeID); @Override Set<StorageLocationReport> getStorageVolumes(UUID datanodeID); double getScmUsedratio(long scmUsed, long capacity);  }### Answer:
@Test public void testIsKnownDatanode() throws SCMException { SCMNodeStorageStatMap map = new SCMNodeStorageStatMap(conf); UUID knownNode = getFirstKey(); UUID unknownNode = UUID.randomUUID(); Set<StorageLocationReport> report = testData.get(knownNode); map.insertNewDatanode(knownNode, report); Assert.assertTrue("Not able to detect a known node", map.isKnownDatanode(knownNode)); Assert.assertFalse("Unknown node detected", map.isKnownDatanode(unknownNode)); }