@Test
public void testCallContextPropagated() {

  ImmutableMap<String, List<String>> extraHeaders =
      ImmutableMap.<String, List<String>>of("header1", ImmutableList.of("value1"));
  ApiCallContext newCallContext = callContext.withExtraHeaders(extraHeaders);
  tracedCallable.clientStreamingCall(outerResponseObsever, newCallContext);
  assertThat(innerCallable.callContext.getExtraHeaders()).isEqualTo(extraHeaders);
}