NoopSpanContextImpl implements NoopSpanContext { @Override public String toSpanId() { return ""; }  @Override String toTraceId(); @Override String toSpanId(); @Override Iterable<Map.Entry<String, String>> baggageItems(); @Override String toString();  }
@Test public void spanIdentifierTest() { SpanContext ctx = NoopSpanContextImpl.INSTANCE; assertEquals("", ctx.toSpanId()); }