public boolean hasAvailableDiskSpace() {
    return NameNodeResourcePolicy.areResourcesAvailable(volumes.values(),
        minimumRedundantVolumes);
  }
@Test
  public void testCheckAvailability()
      throws IOException {
    conf.setLong(DFSConfigKeys.DFS_NAMENODE_DU_RESERVED_KEY, 0);
    NameNodeResourceChecker nb = new NameNodeResourceChecker(conf);
    assertTrue(
        "isResourceAvailable must return true if " +
            "disk usage is lower than threshold",
        nb.hasAvailableDiskSpace());
  }