anchor.diff:  
   -export([compile_iolist/2]).
   -export([unload_code/1]).
  +
  +%% internally used
  +-export([main_in_separate_vm/1]).
   
   %% Include a bunch of tests from gpb_tests.
   %% The shared tests are for stuff that must work both
  
positive.code:       fun(TmpDir) ->
                NEDM = gpb_nif_test_ed1,
                Defs = mk_one_msg_field_of_each_type(),
                {ok, Code} = compile_msg_defs(NEDM, Defs, TmpDir),
                with_tmpcode(
                  NEDM, Code,
                  fun() ->
                          nif_encode_decode_test_it(NEDM, Defs),
                          nif_encode_decode_strings(NEDM, Defs),
  
negative.code:                                   "    repeated bo f2 = 2;",
                                    "}"]),
                Defs = parse_to_proto_defs(DefsTxt),
                {ok, Code} = compile_nif_msg_defs(M, DefsTxt, TmpDir),
                in_separate_vm(
                  TmpDir, M, Code,
                  fun() ->
                          OrigMsg = {ntest1,x,[x,y]},
                          MEncoded  = M:encode_msg(OrigMsg),
  