### Question:
Log4JSegmentListener implements SegmentListener { public void setPrefix(String prefix) { this.prefix = prefix; } Log4JSegmentListener();  Log4JSegmentListener(String prefix); String getPrefix(); void setPrefix(String prefix); @Override void onSetEntity(Entity oldEntity, Entity newEntity); @Override void onClearEntity(Entity entity);  }### Answer:
@Test void testSetPrefix() { Log4JSegmentListener listener = (Log4JSegmentListener) AWSXRay.getGlobalRecorder().getSegmentListeners().get(0); listener.setPrefix(""); Segment seg = new SegmentImpl(AWSXRay.getGlobalRecorder(), "test", TRACE_ID); listener.onSetEntity(null, seg); Assertions.assertEquals(TRACE_ID.toString() + "@" + seg.getId(), ThreadContext.get(TRACE_ID_KEY)); }