code: @Test public void encode(){
    RoutingSupport routing=mock(RoutingSupport.class);
    SessionIdentifierCodec codec=new SimpleSessionIdentifierCodec(routing,null);
    String sessionId="session";
    String result=codec.encode(sessionId);
    assertNull(sessionId,null);
    String route="route";
    codec=new SimpleSessionIdentifierCodec(routing,route);
    result=codec.encode(null);
    assertNull(result);
    String encodedSessionId="session.route";
    when(routing.format(sessionId,route)).thenReturn(encodedSessionId);
    result=codec.encode(sessionId);
    assertSame(encodedSessionId,result);
  }
  