@Test public void checkIt() throws IOException {
  assertThat(ds,instanceOf(Flushable.class));
  assertThat(ds,instanceOf(DataSource.class));
  final FlushableDataSourceHandler handler=FlushableDataSourceHandler.class.cast(Proxy.getInvocationHandler(ds));
  final CommonDataSource delegate=handler.getDelegate();
  assertNotNull(delegate);
  assertFalse(BasicDataSource.class.cast(delegate).isClosed());
  Flushable.class.cast(ds).flush();
  assertTrue(BasicDataSource.class.cast(delegate).isClosed());
  final CommonDataSource newDelegate=handler.getDelegate();
  assertFalse(BasicDataSource.class.cast(newDelegate).isClosed());
  assertNotSame(newDelegate,delegate);
}