test.es6

import mergesort from './index.js';
import expect from 'expect.js';



function randomArray(length) {

  let result = [];

  for (let i = length; i > 0; i -= 1) {
    result.push(parseFloat((Math.random() * 100).toFixed(2)));
  }
  return result;
}

describe('mergesort', () => {
  let desc = (a, b) => b - a;

  it('should sort an unsorted array', () => {
    expect(mergesort([])).to.eql([]);
    expect(mergesort([1])).to.eql([1]);
    expect(mergesort([3, 1])).to.eql([1, 3]);
    expect(mergesort([3, 1, 2])).to.eql([1, 2, 3]);
    expect(mergesort([3, 1, 2, 4])).to.eql([1, 2, 3, 4]);
    expect(mergesort([3, 6, 2, 1])).to.eql([1, 2, 3, 6]);
    expect(mergesort([-3, -6, 2, 1])).to.eql([-6, -3, 1, 2]);
    expect(mergesort([3, 1, 2, 4, 2])).to.eql([1, 2, 2, 3, 4]);
    expect(mergesort([-3, 1, -2, 4, 2])).to.eql([-3, -2, 1, 2, 4]);
  });

  it('should sort using a custom comparator', () => {
    expect(mergesort([], desc)).to.eql([]);
    expect(mergesort([1], desc)).to.eql([1]);
    expect(mergesort([3, 1], desc)).to.eql([3, 1]);
    expect(mergesort([3, 1, 2], desc)).to.eql([3, 2, 1]);
    expect(mergesort([3, 1, 2, 4], desc)).to.eql([4, 3, 2, 1]);
    expect(mergesort([3, 1, 2, 4, 2], desc)).to.eql([4, 3, 2, 2, 1]);
    expect(mergesort([-3, 1, -2, 4, 2], desc)).to.eql([4, 2, 1, -2, -3]);
  });

  it('should not change the unsorted array', () => {
    let unsorted = [-3, 1, -2, 4, 2];
    expect(mergesort(unsorted, desc)).to.eql([4, 2, 1, -2, -3]);
    expect(unsorted).to.eql([-3, 1, -2, 4, 2]);
  });

  it('should work with random array', () => {

    let array = randomArray(100);
    let sorted = mergesort(array);

    for (let i = 0; i < sorted.length - 1; i += 1) {
      expect(sorted[i] <= sorted[i + 1]).to.be.ok();
    }
  });
});