public static boolean fullyDeleteContents(final File dir) {
    return fullyDeleteContents(dir, false);
  }
@Test (timeout = 30000)
  public void testFullyDeleteContents() throws IOException {
    boolean ret = FileUtil.fullyDeleteContents(del);
    Assert.assertTrue(ret);
    Verify.exists(del);
    Assert.assertEquals(0, Objects.requireNonNull(del.listFiles()).length);
    validateTmpDir();
  }