module.exports = [{
  id: 1,
  children: [{
    id: 2,
    children: [{
      id: 3
    }]
  }]
}, {
  id: 4
}];

module.exports = [{
  id: 1,
  parent_id: null,
  children: [{
    id: 2,
    parent_id: 1,
    children: [{
      id: 3,
      parent_id: 2
    }]
  }]
}, {
  id: 4,
  parent_id: null
}];

Add missing property to expected fixture