public Map<Identifier, Item> asMap() {
    return entries;
  }
@Test
  public void testAsMap() {
    DisplayData data =
        DisplayData.from(
            new HasDisplayData() {
              @Override
              public void populateDisplayData(DisplayData.Builder builder) {
                builder.add(DisplayData.item("foo", "bar"));
              }
            });

    Map<DisplayData.Identifier, DisplayData.Item> map = data.asMap();
    assertEquals(1, map.size());
    assertThat(data, hasDisplayItem("foo", "bar"));
    assertEquals(map.values(), data.items());
  }