@Test
public void timeoutTriggered_headerValue_headerValuePartOfCallback() {

    // given
    TimeoutExpirationCallback expiredCallback = mock(TimeoutExpirationCallback.class);
    sut.addExpiredCallback(expiredCallback);
    // when
    requestAndTriggerTimeout();
    // then
    ArgumentCaptor<TimeoutExpirationContext> captor = ArgumentCaptor.forClass(TimeoutExpirationContext.class);
    verify(expiredCallback).expired(isA(Timeout.class), captor.capture());
    Map<HeaderName<?>, Object> headers = captor.getValue().getOriginalHeaders();
    assertThat("Expected header value in callback param.", headers.get(DEFAULT_HEADER), equalTo(DEFAULT_HEADER_VALUE));
}