@Test
  public void putThenResetThenPutAgain() throws Exception {
    mbf.put("hello");
    mbf.put("hello");
    mbf.resetHead();
    mbf.put("hello");
    assertFalse(mbf.mightContain("hello"));

    mbf.put("hello");
    assertTrue(mbf.mightContain("hello"));
    mbf.resetHead();
    assertFalse(mbf.mightContain("hello"));
  }
 @Test
 public void multipleHeadResetsIsImportant() throws Exception {
   mbf.put("hello");
   mbf.put("hello");
   mbf.resetHead();
   mbf.resetHead();
   mbf.put("hello");
   assertFalse(mbf.mightContain("hello"));
   mbf.put("hello");
   assertFalse(mbf.mightContain("hello"));
   mbf.put("hello");
   assertTrue(mbf.mightContain("hello"));
 }