Add option to render to enable improved ember-engines testing API

[villander]

Add a second argument to render helper that can be used to specify a custom owner to be used for the provided template. This allows ember-engines to provide customized test setup code that users can use
to build and Engine instance and perform simpler rendering tests that from the context of that Engine.

When coupled with changes in ember-engines itself (ember-engines/ember-engines#653), an API similar to the following will be possible:

  module('setupEngineTest', function (hooks) {
    setupTest(hooks);
    setupEngine(hooks, 'my-engine-name');

    test('it exists', function (assert) {
      assert.expect(1);

      let route = this.engine.lookup('route:post.likes');
      assert.ok(route);
    });
  });

  module('setupEngineRenderingTest', function (hooks) {
    setupRenderingTest(hooks);
    setupEngine(hooks, 'my-engine-name');

    test('should change colors', async function(assert) {
      assert.expect(2);

      // set the outer context to red
      this.set('colorValue', 'red');

      await render(hbs`{{pretty-color name=colorValue}}`, { owner: this.engine });

      assert.equal(this.element.querySelector('div').getAttribute('style'), 'color: red', 'starts as red');

      this.set('colorValue', 'blue');

      assert.equal(this.element.querySelector('div').getAttribute('style'), 'color: blue', 'updates to blue');
    });
  });

[ef4]

Sorry, I was looking at only one of your commits, not all of them. And I was also reacting the code you pasted here in the comments, which I didn't realize isn't actually code in your PR.

[rwjblue]

We've landed a bunch of fixes to make CI more consistent (dropping Node < 10, reroll yarn.lock, etc), probably needs a rebase to kick things off again.

[villander]

@rwjblue any chance to have a look here to make a progress?

[rwjblue]

I think this is good to go now!! Thanks @villander @richgt!

[rwjblue]

FWIW, this is what the normal router setup would do for creating an engine instance.

https://github.com/emberjs/ember.js/blob/955a5e6ff2202de59506db288f7fb263882d1b9c/packages/%40ember/-internals/routing/lib/system/router.ts#L1340-L1376