text: import { equal, deepEqual } from 'assert';
  import fold from '../fold';
  
  let sub = (x, y) => x - y;
  test('#fold', () => {
  	let arr = [1, 2, 3, 4];
  	equal(fold(sub, 8, arr), -2);
  	deepEqual(arr, [1, 2, 3, 4]);
  });
  