Specify detail component should display model fields

We add a component test that reproduces the acceptance test error: we specify that the component displays the post's title. And we go ahead and specify that it displays the body, too, because that seems safe in this case.

Inner red:
✘ Element .js-post-detail-title exists
✘ Element .js-post-detail-body exists

This means that the title field was not found, to be able to retrieve the textContent from it.

tests/integration/components/post-detail-test.js

@@ -6,21 +6,15 @@ import hbs from 'htmlbars-inline-precompile';
 module('Integration | Component | post-detail', function(hooks) {
   setupRenderingTest(hooks);
 
-  test('it renders', async function(assert) {
-    // Set any properties with this.set('myProperty', 'value');
-    // Handle any actions with this.set('myAction', function(val) { ... });
+  test('it displays details for the passed-in post', async function(assert) {
+    this.set('testModel', {
+      title: 'Test Title',
+      body: 'This is a test post!',
+    });
 
-    await render(hbs`{{post-detail}}`);
+    await render(hbs`{{post-detail post=testModel}}`);
 
-    assert.equal(this.element.textContent.trim(), '');
-
-    // Template block usage:
-    await render(hbs`
-      {{#post-detail}}
-        template block text
-      {{/post-detail}}
-    `);
-
-    assert.equal(this.element.textContent.trim(), 'template block text');
+    assert.dom('.js-post-detail-title').hasText('Test Title');
+    assert.dom('.js-post-detail-body').hasText('This is a test post!');
   });
 });