Add Test Cases to Cartomancy mini-app

[gilkeidar]

Task Description: Add Jest unit tests to the Cartomancy mini-app.

• [ ] In the tests directory, create the subdirectory cartomancy.
• [ ] Add at least one file (e.g. cartomancy.test.js)
• [ ] Write unit tests to check the functionality of your code

Note: You cannot call fetch() in Jest unit tests. This includes testing whether a JSON file was read correctly by the FortuneEngine.

If you want to test a feature that relies on the FortuneEngine, do the following:

  //  Create a FortuneEngine object
  const engine = new FortuneEngine('Test');

  //  Can't test fetch() in Jest - assume read.
  engine.initialized = true;

  //  Set JSON contents
  const jsonContents = {
      // insert your JSON file's contents here
  };

  engine.json_contents = jsonContents;

  const outcomes = engine.json_contents['option-result pair'];

  engine.outcomes = outcomes;

  // can safely call get_random_subset() now

Is it gross? Yes. But Jest is made for unit testing - I believe we need end-to-end testing support to facilitate testing of this kind.