export default function chunk(arr, size){
  if(!Array.isArray(arr) || size <= 0) return [];
  const out = [];
  for(let i = 0; i <= arr.length; i += size){
    out.push(arr.slice(i, i + size));
  }
  return out;
}

import chunk from './js-debug-off-by-one';

describe('chunk', () => {
  test('keeps the last partial group', () => {
    expect(chunk([1,2,3,4,5], 2)).toEqual([[1,2],[3,4],[5]]);
  });

  test('does not append an empty group when the length divides evenly', () => {
    expect(chunk([1,2,3,4], 2)).toEqual([[1,2],[3,4]]);
  });

  test('returns [] for an empty array', () => {
    expect(chunk([], 3)).toEqual([]);
  });

  test('returns [] for invalid size or non-array input', () => {
    expect(chunk([1,2,3], 0)).toEqual([]);
    // @ts-ignore
    expect(chunk(null, 2)).toEqual([]);
  });
});