to contain focused element matching (DOMElement)

Assert that a child element is the currently focused element on the page.

var document = createDocument(`
  <form>
  <label>
    <span>Name</span>
    <input type="text">
  </label>
  <button>Submit</button>
  </form>
`);
 
var button = document.querySelector('button');
button.focus();
 
expect(document, 'to contain focused element matching', 'button');

In case of a failing expectation you get the following output:

button.blur();
expect(document, 'to contain focused element matching', 'button');

expected <html><head></head><body>...</body></html>
to contain focused element matching 'button'
  expected <button>Submit</button> to have focus