public PTransform<InputT, OutputT> setDisplayData(@NonNull List<ItemSpec<?>> displayData) {
    this.displayData = displayData;
    return this;
  }
@Test
  public void testSetDisplayData() {
    PTransform<PCollection<String>, PCollection<String>> transform =
        new PTransform<PCollection<String>, PCollection<String>>() {
          @Override
          public PCollection<String> expand(PCollection<String> begin) {
            throw new IllegalArgumentException("Should never be applied");
          }
        };
    transform.setDisplayData(
        ImmutableList.of(DisplayData.item("key1", "value1"), DisplayData.item("key2", 2L)));

    final DisplayData displayData = DisplayData.from(transform);
    assertThat(displayData.items(), hasSize(2));
    assertThat(displayData, hasDisplayItem("key1", "value1"));
    assertThat(displayData, hasDisplayItem("key2", 2L));
  }