React-modal: Create testing examples

[claydiffrient]

Because testing seems to be less understood than many other things we should create a few examples of testing for people to see.

I think the biggest thing people want to test is opening the modal and asserting various facts about the contents of the modal.

We should create examples for the following:

• [ ] Mocha
  
  
  
  • [ ] Enzyme
  
  
  • [ ] React TestUtils
  
  
• [ ] Jest

[aziz]

Please provide some examples on how to access the portal using enzyme

[hawyangpeng]

https://github.com/airbnb/enzyme/issues/252#issuecomment-266125422

[ollwenjones]

"jest" involves snapshot example with react-test-renderer ?

[ollwenjones]

if this helps anyone, I had to add a dummy app element to get around the App element is not defined error in Jest:

  let app = document.createElement('div');
  app.id = 'app';

  document
    .getElementsByTagName('body')
    .item(0)
    .appendChild(app);

  Modal.setAppElement('#app');

[ollwenjones]

@aziz I ended up piping some innerHTML to jest snapshots, but I did find this helpful:

http://remarkablemark.org/blog/2017/05/17/testing-react-modal/