@Test
  public void testLeaseRenew() throws IOException {
    DFSClient client = FS.getClient();
    assertFalse(client.renewLease());

    FanOutOneBlockAsyncDFSOutput out = create("/test_lease_renew");
    assertTrue(client.renewLease());
    client.closeAllFilesBeingWritten(false);
    assertTrue(out.isClosed());

    assertFalse(client.renewLease());

    out = create("/test_lease_renew");
    assertTrue(client.renewLease());
    client.closeAllFilesBeingWritten(true);
    assertTrue(out.isClosed());
  }
Make sure lease renewal works. Since it is in a background thread, normal read/write test can not
verify it.
<p>
See HBASE-28955 for more details.
hbase-asyncfs/src/test/java/org/apache/hadoop/hbase/io/asyncfs/TestLeaseRenewal.java