text: import { assert } from 'chai';
  
  import { levelOrder, TreeNode } from './index';
  
  describe('levelOrder', function() {
    it ('always true', () => {
      assert.equal(true, true);
    });
  
    it ('level-order', () => {
      const t15 = new TreeNode(15, null, null);
      const t7 = new TreeNode(7, null, null);
      const t20 = new TreeNode(20, t15, t7);
      const t9 = new TreeNode(9, null, null);
      const t3 = new TreeNode(3, t9, t20);
      assert.deepEqual(levelOrder(t3), [
        [3],
        [9,20],
        [15,7]
      ]);
    });
  
    it ('level-order', () => {
      assert.deepEqual(levelOrder(null), []);
    });
  });
  