@Test(expected = IllegalArgumentException.class)
 public void testSeedNotDistinct() {
   crawler = new MockWebCrawler(0, 1);
   crawler.crawl("http://www.bbc.co.uk/", "seedNotUnique.txt");
 }
 @Test
 public final void testSearch() throws Exception {
   assertTrue(crawler.search(urlTrue));
   assertFalse(crawler.search(urlFalse));
 }