anchor.diff:  
   void _writeModule(String outPath, String expectPath, JSModuleFile result) {
     _ensureDirectory(path.dirname(outPath));
  -  _ensureDirectory(path.dirname(expectPath));
   
     String errors = result.errors.join('\n');
     if (errors.isNotEmpty && !errors.endsWith('\n')) errors += '\n';
  
positive.code: 
    var jsFile = new File(outPath + '.js');
    var summaryFile = new File(outPath + '.sum');
    var expectFile = new File(expectPath + '.js');
    var errorFile = new File(outPath + '.err');
  
    if (result.isValid) {
  
negative.code:     var relativePath = path.relative(testFile, from: codegenTestDir);
  
      // Only compile the top-level files for generating coverage.
      bool isTopLevelTest = path.dirname(relativePath) == ".";
      if (codeCoverage && !isTopLevelTest) continue;
  
      var name = path.withoutExtension(relativePath);
      test('dartdevc $name', () {
        // Check if we need to use special compile options.
        var contents = new File(testFile).readAsStringSync();
        var match =
  