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React 16 fragments (rendering arrays and strings) unsupported

See original GitHub issue

React 16 added a new return type of an array with many fragments of JSX, see React 16 blog post

Enzyme v3.0.0 with React 16 adapter 1.0.0 throws an error with this sample code

Error

/node_modules/react-dom/cjs/react-dom-server.node.development.js:2776
    var tag = element.type.toLowerCase();
                          ^

TypeError: Cannot read property 'toLowerCase' of undefined

Failing test

import Adapter from 'enzyme-adapter-react-16';
import { configure, shallow } from 'enzyme';
import React from 'react';
import test from 'tape';

function Fragments() {
  return [
    <li key="A">First item</li>,
    <li key="B" id="item">Second item</li>,
    <li key="C">Third item</li>
  ];
}

test('One element parent', (assert) => {
  configure({ adapter: new Adapter() });

  const wrapper = shallow(<Fragments />);

  const actual = wrapper.html();
  const expected = undefined;
  assert.notEqual(actual, expected, 'Has ID selector');

  assert.end();
});

Passing test

import Adapter from 'enzyme-adapter-react-16';
import { configure, shallow } from 'enzyme';
import React from 'react';
import test from 'tape';

function NotFragments() {
  return (
    <ul>
      <li key="A">First item</li>,
      <li key="B" id="item">Second item</li>,
      <li key="C">Third item</li>
    </ul>
  );
}

test('One element parent', (assert) => {
  configure({ adapter: new Adapter() });

  const wrapper = shallow(<NotFragments />);

  const actual = wrapper.find('#item').is('li');
  const expected = true;
  assert.equal(actual, expected, 'Has ID selector');

  assert.end();
});

-=Dan=-

Issue Analytics

State:
Created 6 years ago
Reactions:55
Comments:32 (8 by maintainers)

Top GitHub Comments

17reactions

echenleycommented, Oct 24, 2017

Temporary hack that seems to work well enough:

const component = shallow(<FragmentComponent />)
const fragment = component.instance().render()
expect(shallow(<div>{fragment}</div>).getElement()).toMatchSnapshot()

12reactions

tkrotoffcommented, Feb 7, 2018

Best solution I’ve found so far: wrap fragments with <div> for the tests only.

class MyComponent {
  render() {
    return (
      <>
        <div>Foo</div>
        <div>Bar</div>
      </>
    );
  }
}

class MyComponentEnzymeFix extends MyComponent {
  render() {
    return <div>{super.render()}</div>;
  }
}

const wrapper = mount(<MyComponentEnzymeFix />); // Instead of mount(<MyComponent />)

        // instead of .toEqual('     <div>Foo</div><div>Bar</div>     ')
expect(wrapper.html()).toEqual('<div><div>Foo</div><div>Bar</div></div>');