Task 3: Message Class

Up to this point, you have got a copy of the starter code and taken an initial dive into how the Command class works. Now let’s turn our focus to the Message class!


Recall, the role of a message object is to bundle commands to send to the rover.

Remember with TDD, first read through the description of the class. Then read through the given tests and think about what each test means for the desired behavior of the class. Only then should you start coding the Message class.

Message Class Description

  1. This class builds an object with two properties.
    1. constructor(name, commands)
      1. name is a string that is the name of the message.
      2. commands is an array of Command objects.
let commands = [new Command('MODE_CHANGE', 'LOW_POWER'), new Command('STATUS_CHECK')];
let message = new Message('Test message with two commands', commands);

Message Tests

At the same level as command.spec.js, look for a file called message.spec.js and read the unit tests for the Message class as described below. After reading about the tests, add the necessary code to the Message class.

Test 4

This test description is “throws error if a name is NOT passed into the constructor as the first parameter”. Review the first test in command.spec.js for an example of how this test works.

  1. Look at the code in command.js. Use that to help you write the Message class in message.js so that your test passes. Refer to the Message Class description above for more details.

Test 5

The description is “constructor sets name”. The test confirms that the constructor in the Message class correctly sets the name property in a new message object.

Test 6

The description reads “contains a commands array passed into the constructor as the 2nd argument”. This test confirms that the commands property of a new message object contains the data passed in from the Message(name, commands) call.


You are moving onto the red planet now. Be prepared for fewer instructions.

The final class we need to work on is Rover. Let’s check it out in the Rover Class section .