ember testing component with yield

I cannot get the compiled html to be inputted into the component via the yield block expression. See test:

import { moduleForComponent, test } from 'ember-qunit';

moduleForComponent('pro-tab-link', 'Unit | Component | pro tab link', {
  // Specify the other units that are required for this test
  // needs: ['component:foo', 'helper:bar'],
  unit: true
});

test('it renders', function(assert) {
  assert.expect(3);

  // Creates the component instance
  var component = this.subject({
    template: Ember.Handlebars.compile(
      "<h1>Hello world</h1>"
    )
  });

  console.log(component);
  assert.equal(component._state, 'preRender');

  var $component = this.append();

  Ember.run(function() {
   component.set('isOpen', true);
 });

  console.log(component);
  console.log($component.html());

  assert.equal(component._state, 'inDOM');
  assert.ok(component.isOpen);
});

And the template:

if isOpen
  == yield

For some reason, the h1 tag is not being passed into the yield of the component. How do I get this working?