@Test
  public void testCacheIsUsed() throws IOException, InvalidRangeException {
    String filename = "file:TestAggExistingCache.xml";
    System.out.printf("%s%n", filename);

    String cacheDirName = TestDir.temporaryLocalDataDir + "testAggExistingCache/";
    System.out.printf("cacheDir=%s%n", cacheDirName);
    File cacheDir = new File(cacheDirName);
    FileUtils.deleteDirectory(cacheDir); // from commons-io
    assert !cacheDir.exists();

    DiskCache2 cache = new DiskCache2(cacheDirName, false, 0, 0);
    cache.setAlwaysUseCache(true);
    Assert.assertEquals(cache.getRootDirectory(), cacheDirName);
    assert new File(cache.getRootDirectory()).exists();

    Aggregation.setPersistenceCache(cache);
    AggregationExisting.countCacheUse = 0;

    try (NetcdfFile ncfile = NcMLReader.readNcML(new StringReader(ncml), filename, null)) {
      System.out.println(" TestNcmlAggExisting.open " + filename);
      Array ATssta = ncfile.readSection("ATssta(:,0,0,0)");
      Assert.assertEquals(4, ATssta.getSize());
    }
    Assert.assertEquals(0, AggregationExisting.countCacheUse);
    AggregationExisting.countCacheUse = 0;

    try (NetcdfFile ncfile = NcMLReader.readNcML(new StringReader(ncml), filename, null)) {
      System.out.println(" TestNcmlAggExisting.open " + filename);
      Array ATssta = ncfile.readSection("ATssta(:,0,0,0)");
      Assert.assertEquals(4, ATssta.getSize());
    }
    Assert.assertEquals(8, AggregationExisting.countCacheUse);
  }