Node, Mocha: Simple test suite for Rooster object with Mocha and Node asserts methods. (https://mochajs.org, https://nodejs.org/api/assert.html).

rooster.js

// Define a rooster
Rooster = {};

// Return a morning rooster call
Rooster.announceDawn = () => {
  return 'moo!';
}

// Return hour as string
// Throws Error if hour is not between 0 and 23 inclusive
Rooster.timeAtDawn = (hour) => {
  if (hour < 0 || hour > 23) {
    throw new RangeError;
  } else {
    return hour.toString();
  };
}

module.exports = Rooster;

rooster_test.js

/**
* More https://mochajs.org/#examples
*/
const assert = require('assert');
const Rooster = require('./rooster.js');

describe('string', () => {
  describe('string', () => {
    it('returns a rooster call', () => {
      //Setup
      const expected = 'blablabla';
      //exercise
      const actual = Rooster.announceDawn();
      //verify
      assert.strictEqual(typeof actual, typeof expected);
    });
    
    it('returns its argument as a string', () => {
      //setup
      const expected = 'blablabla';
      //exercise
      const actual = Rooster.timeAtDawn(14);
      //verify
      assert.strictEqual(typeof actual, typeof expected);
    })
    
    it('throws an error if passed a number less than 0', () => {
      //setup & exercise
      const hour = -1;
      //verify
      assert.throws(
        () => {
           Rooster.timeAtDawn(hour);
        },
        RangeError
      );
    });
    
    it('throws an error if passed a number greater than 23', () => {
      //setup & exercise
      const hour = 24;
      //verify
      assert.throws(
        () => {
           Rooster.timeAtDawn(hour);
        },
        RangeError
      );
    });
  });
});