code: @Test public void testAdd(){
    HeaderValues headerValues=new HeaderValues(Headers.HOST);
    assertTrue(headerValues.add("Foo"));
    assertTrue(headerValues.contains("Foo"));
    assertTrue(headerValues.contains(new String("Foo")));
    assertFalse(headerValues.contains("Bar"));
    assertFalse(headerValues.isEmpty());
    assertEquals(1,headerValues.size());
    assertEquals("Foo",headerValues.peek());
    assertEquals("Foo",headerValues.peekFirst());
    assertEquals("Foo",headerValues.peekLast());
    assertEquals("Foo",headerValues.get(0));
    assertTrue(headerValues.offerFirst("First!"));
    assertTrue(headerValues.contains("First!"));
    assertTrue(headerValues.contains("Foo"));
    assertEquals(2,headerValues.size());
    assertEquals("First!",headerValues.peek());
    assertEquals("First!",headerValues.peekFirst());
    assertEquals("First!",headerValues.get(0));
    assertEquals("Foo",headerValues.peekLast());
    assertEquals("Foo",headerValues.get(1));
    assertTrue(headerValues.offerLast("Last!"));
    assertTrue(headerValues.contains("Last!"));
    assertTrue(headerValues.contains("Foo"));
    assertTrue(headerValues.contains("First!"));
    assertEquals(3,headerValues.size());
    assertEquals("First!",headerValues.peek());
    assertEquals("First!",headerValues.peekFirst());
    assertEquals("First!",headerValues.get(0));
    assertEquals("Foo",headerValues.get(1));
    assertEquals("Last!",headerValues.peekLast());
    assertEquals("Last!",headerValues.get(2));
  }
  