anchor.diff:    future.then((process) {
       Expect.isNotNull(process.pid);
       Expect.isTrue(process.pid is int);
  -    Expect.isNull(process.exitCode);
  -    Expect.isNull(process.stderr);
  -    Expect.isNull(process.stdin);
  -    Expect.isNull(process.stdout);
  +    Expect.throwsStateError(() => process.exitCode);
  +    Expect.throwsStateError(() => process.stderr);
  +    Expect.throwsStateError(() => process.stdin);
  +    Expect.throwsStateError(() => process.stdout);
       Expect.isTrue(process.kill());
     }).whenComplete(() {
       asyncEnd();
  
positive.code: import "package:async_helper/async_helper.dart";
  import "package:expect/expect.dart";
  
  import "process_test_util.dart";
  
  void test() {
    asyncStart();
    var script =
  
negative.code:   future.then((process) {
      Expect.isNotNull(process.pid);
      Expect.isTrue(process.pid is int);
      Expect.throwsStateError(() => process.exitCode);
      var message = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
      process.stdin.add(message);
      process.stdin.flush().then((_) => process.stdin.close());
  