@Test
  public void testGetPeerForFileCopyWithLeaderNotFound() {
    MockPartitionId partitionId = new MockPartitionId(123456, "RANDOM_PARTITION_CLASS");
    ReplicaId replicaId = FileCopyUtils.getPeerForFileCopy(partitionId, "datacenter");
    assertNull(replicaId);
  }
Test for {@link FileCopyUtils#getPeerForFileCopy(PartitionId, String)}
Test if no LEADER replica is found in the given datacenter.
ambry-file-transfer/src/test/java/com/github/ambry/filetransfer/FileCopyUtilsTest.java