@Test public void decorate_parent() {

  TraceContext decorated = propagationFactory.decorate(context);
  BasicMapExtra extra1 = decorated.findExtra(BasicMapExtra.class);
  extra1.put("1", "one");
  context2 = propagationFactory.decorate(context2.toBuilder().addExtra(extra1).build());
  BasicMapExtra extra2 = context2.findExtra(BasicMapExtra.class);
  assertThat(context2.extra()).containsExactly(extra2); // didn't duplicate
  assertThat(extra2.get("1")).isEqualTo("one");
  assertExtraClaimed(context2);
}