anchor.diff:  
   import "dart:io";
   
  +const _SCRIPT_KEY = '_test_script';
  +
   void expectEquals(a, b) {
     if (a != b) {
       throw 'Expected: $a\n'
  
positive.code: }
  
  void verify(String exePath, {String altPath}) {
    var env = {'SCRIPT': 'yes'};
    if (altPath != null) {
      env['PATH'] = altPath;
    }
  
negative.code: String get scriptPath => Platform.script.toFilePath();
  
  void main() {
    if (Platform.environment.containsKey(_SCRIPT_KEY)) {
      print(Platform.executable);
      return;
    }
  