old_contents: //
  // This is only a SKELETON file for the 'Hello World' exercise. It's been provided as a
  // convenience to get you started writing code faster.
  //
  
  class HelloWorld {
    hello() {
      //
      // YOUR CODE GOES HERE
      //
    }
  }
  
  export default HelloWorld;
  
new_contents: //
  // This is only a SKELETON file for the 'Hello World' exercise. It's been provided as a
  // convenience to get you started writing code faster.
  //
  
  class HelloWorld {
    hello() {
      return "Hello, World!";
    }
  }
  
  export default HelloWorld;
  
subject: Return helloworld