Ember tests/Mirage not finding DOM elements

I'm trying to do some basic acceptance tests in Ember, using Mirage. I'm using only fixtures at this point to populate the test environment, just to find my feet. When I run ember in the test environment (i.e., with -e test), I can see my app is populating with expected data. And the DOM has some buttons, etc. All is well.

However, when I run a test to visit a page and click a button, the test is telling me it can't find the button. In other words, running -e test and checking localhost shows the app seems to be fine. But then checking localhost/tests has a test failing saying it can't find a button that is definitely there in the -e test screen.

I've confirmed that the button exists in the -e test environment, using both inspector and just issuing a basic jquery select at the console line.

So I assume there's something wrong in the setup or somewhere in a configuration?

In particular:

module('Acceptance | basic tests', {
  beforeEach: function() {
    this.application = startApp();
  },

  afterEach: function() {
    Ember.run(this.application, 'destroy');
  }
});

test('visiting /orders', function(assert) {
  visit('/orders');

  andThen(function() {
    assert.equal(currentURL(), '/orders');
  });
});

test('visiting /basic', function(assert) {
  visit('/orders');
  click('top-row-orders-button'); //button.top-row-orders-button fails too
  andThen(function() {
    assert.equal(currentURL(), '/orders');
  });
});

The first test (just visiting the url) passes. The second test is where it says it can't find the button. And again, when I serve -e test, and enter this at the console: $('.top-row-orders-button') it returns the button in question.

Happy to provide any more info anyone needs. Would appreciate any help. I've been banging my head on this for a few days now with no luck.