### Question:
SLF4JSegmentListener implements SegmentListener { public void setPrefix(String prefix) { this.prefix = prefix; } SLF4JSegmentListener();  SLF4JSegmentListener(String prefix); String getPrefix(); void setPrefix(String prefix); @Override void onSetEntity(Entity oldEntity, Entity newEntity); @Override void onClearEntity(Entity entity);  }### Answer:
@Test public void testSetPrefix() { SLF4JSegmentListener listener = (SLF4JSegmentListener) AWSXRay.getGlobalRecorder().getSegmentListeners().get(0); listener.setPrefix(""); Segment seg = new SegmentImpl(AWSXRay.getGlobalRecorder(), "test", traceID); listener.onSetEntity(null, seg); Assert.assertEquals(traceID.toString() + "@" + seg.getId(), MDC.get(TRACE_ID_KEY)); }