@Test public void allKeyNames_extraFieldPropagation() {

  ExtraFieldPropagation.Factory factory =
    ExtraFieldPropagation.newFactory(B3SinglePropagation.FACTORY, "user-id", "session-id");
  assertThat(BaggagePropagation.allKeyNames(factory.get()))
    .containsExactly("b3", "user-id", "session-id");
}