@Test
public void testExpire() throws InterruptedException {

	ExpiringSet<String> expiringSet = new ExpiringSet<String>(2);   // seconds
	assertFalse(expiringSet.contains("hello"));
	assertTrue(expiringSet.contains("hello"));
	Thread.sleep(3 * 1000);
	assertFalse(expiringSet.contains("hello"));
	assertTrue(expiringSet.contains("hello"));
}