anchor.diff:      %%
       ?P("send/4: S2 -> S1"),
       ok = gen_udp:send(S2, {Addr,P1}, [], <<"klmno">>),
  +    ?SLEEP(100),
  +
       ?P("send/3: S1 -> S2"),
       ok = gen_udp:send(S1, {Family,{loopback,P2}}, <<"pqrst">>),
  +    ?SLEEP(100),
  +
       TestSend andalso
           begin
               ?P("send/4: S1 -> S2"
                  "~n   ~p", [OptsVals]),
  -            ok = gen_udp:send(S1, {Family,{loopback,P2}}, OptsVals2, <<"PQRST">>)
  +            ok = gen_udp:send(S1,
  +                              {Family,{loopback,P2}}, OptsVals2, <<"PQRST">>),
  +            ?SLEEP(100)
           end,
  +
       ?P("try recv data on S1"),
       {ok,{_,P2,<<"klmno">>}} = gen_udp:recv(S1, 0, Timeout),
       ?P("await message on S2"),
  
positive.code:     %%
      ?P("send/3: S2 -> S1"),
      ok = gen_udp:send(S2, {Addr,P1}, <<"abcde">>),
      ?P("send/4: S1 -> S2"),
      ok = gen_udp:send(S1, Addr, P2, <<"fghij">>),
      TestSend andalso
  
negative.code:             {ok,{_,P2,OptsVals0,<<"ABCDE">>}} = gen_udp:recv(S1, 0, Timeout),
              ?P("S1 recv: "
                 "~n   OptsVals0: ~p", [OptsVals0]),
              ?SLEEP(100),
  
              ?P("try S1 recv"),
              {ok,{_,P2,OptsVals1,<<"12345">>}} = gen_udp:recv(S1, 0, Timeout),
              ?P("S1 recv: "
                 "~n   OptsVals1: ~p", [OptsVals1]),
              ?SLEEP(100),
              verify_sets_eq(OptsVals0, OptsVals),
              verify_sets_eq(OptsVals1, OptsVals)
          end,
  