anchor.diff:   */
   class TestCase {
     /**
  -   * A list of commands to execute. Most test cases have a single command. 
  +   * A list of commands to execute. Most test cases have a single command.
      * Dart2js tests have two commands, one to compile the source and another
      * to execute it. Some isolate tests might even have three, if they require
      * compiling multiple sources that are run in isolation.
  
positive.code: 
  
  /**
   * CommandOutput records the output of a completed command: the process's exit 
   * code, the standard output and standard error, whether the process timed out,
   * and the time the process took to run.  It also contains a pointer to the
   * [TestCase] this is the output of.
  
negative.code:     arguments.add(htmlFile);
      return arguments;
    }
  
    Path get expectedOutputFile => expectedOutputPath;
    bool get isPixelTest => (expectedOutputFile != null &&
                             expectedOutputFile.filename.endsWith(".png"));
  