anchor.diff:  
   library fasta.test.compile_platform_test;
   
  +import 'dart:async';
   import 'dart:io';
   
   import 'package:async_helper/async_helper.dart';
  
positive.code:   });
  }
  
  withTemporyDirectory(String prefix, Future f(Uri tmp)) async {
    Directory tmp = await Directory.systemTemp.createTemp(prefix);
    try {
      await f(tmp.uri);
  
negative.code: 
  main(List<String> arguments) async {
    await asyncTest(() async {
      await withTemporaryDirectory("compile_platform_test_", (Uri tmp) async {
        String patchedSdk = Uri.base
            .resolveUri(new Uri.file(Platform.resolvedExecutable))
            .resolve("patched_sdk")
  