Add Concept Exercise for 'randomness': Captain's Log

[quintuple-mallard]

This PR adds hints.md,introduction.md, instructions.md, config.json, design.md, exemplar.js, captains-log.js, and captains-log.spec.js to a new exercise on the JavaScript track.

A couple of questions to a reviewer:

• The other exercises have these files:
  .gitignore, .npmrc, LICENSE, package.json, jest.config.js, global.d.ts, eslint.config.mjs, and babel.config.js. These are not mentioned in the docs though. Should I add these, or does that happen automatically somehow?
• How do I generate a UUID?

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[Cool-Katt]

If you've used configlet, which is our tool for managing tracks and things like generating exercices, then all the needed files should be auto-generated and you shouldn't need to manually attach a UUID, but in case you do configlet can also do that.

Also worth checking out our (slightly outdated) CONTRIBUTING guide.

[Cool-Katt]

You probably want to use toMatch here.

[Cool-Katt]

I would have liked to see repeated testing like this in a for loop or something similar, so you can avoid repetition and we can test an arbitrary amount of times, because randomness is tricky.

Additionally, this - (41000<=randomStardate()<42000) is not valid JS syntax (technically it is but it doesn't work like in Python), because chained comparison isn't supported like that. You'll need something like (41000 <= stardate && stardate < 42000) instead.

[SleeplessByte]

I think this will work:

function loadDie(...values) {
  const originalRandom = Math.random()
  
  Math.random = function loadedDie { 
    if (values.length === 0) {
      return originalRandom();
    }
    
    return values.shift();
  }

  return () => {
    Math.random = originalRandom;
  }
}

describe('randomStardate',() => {
  test('stardate is between 41000 and 42000',() => {
    const restore = loadDie(
      0, 0, 0, 0, 0, 0,
      1, 1, 1, 1, 1, 1,
      0.5, 0.5, 0.5, 0.5, 0.5, 0.5
    );
    
    // 6 * 0, 6 * 1, 6 * 0.5 and everything else random
    
    for (let i = 0; i < 10_000; i++) {
      const starDate = randomStardate()
      expect(starDate).toBeGreaterThanOrEqual(41_000);
      expect(starDate).toBeLessThan(42_000);
    }
  
    restore();
  }
}

This should run in ~ 0.1 ms

[quintuple-mallard]

Errors in tests fixed, and for loops now used.

Just a question - is there a toInclude method?

[SleeplessByte]

(I wrote an entire thesis on how to calculate the expected number of rolls to get all the values in the planet class thing, but when I tried to submit it I pressed back accidentally and then lost it all. Will write it again soon...)

[SleeplessByte]

I think this will work:

function loadDie(...values) {
  const originalRandom = Math.random()
  
  Math.random = function loadedDie { 
    if (values.length === 0) {
      return originalRandom();
    }
    
    return values.shift();
  }

  return () => {
    Math.random = originalRandom;
  }
}

describe('randomStardate',() => {
  test('stardate is between 41000 and 42000',() => {
    const restore = loadDie(
      0, 0, 0, 0, 0, 0,
      1, 1, 1, 1, 1, 1,
      0.5, 0.5, 0.5, 0.5, 0.5, 0.5
    );
    
    // 6 * 0, 6 * 1, 6 * 0.5 and everything else random
    
    for (let i = 0; i < 10_000; i++) {
      const starDate = randomStardate()
      expect(starDate).toBeGreaterThanOrEqual(41_000);
      expect(starDate).toBeLessThan(42_000);
    }
  
    restore();
  }
}

This should run in ~ 0.1 ms

[SleeplessByte]

Just a question - is there a toInclude method?

Yes: toContain(item)