title: Ember simple auth tests failing intermittently
body: <p>I am struggling to debug failing tests on an Ember 3.0 app. I have a login form using ember-simple-auth. The authenticate action looks like this:</p>
  
  <pre><code>let { identification, password } = this.getProperties('identification', 'password');
  this.get('session').authenticate('authenticator:devise', identification, password)
  .catch((reason) =&gt; {
      this.set('loginError', reason.errors || reason);
  });
  </code></pre>
  
  <p>My test simply fills in the form and clicks a button to trigger this action, then checks a user is logged in:</p>
  
  <pre><code>invalidateSession();
  await visit('/');
  
  fillIn('#identification', 'test@email.com');
  fillIn('#password', 'secret');
  await click('.login-btn');
  
  let sesh = currentSession();
  let isAuthed = get(sesh, 'isAuthenticated');
  assert.equal(
    isAuthed,
    true,
    'after a user submits good creds to login form, they are logged in'
  );
  </code></pre>
  
  <p>Using a Mirage backend, this works every time. However, using a Rails API which returns the same response, this test fails about half the time. It seems to be random whether it will pass or fail. </p>
  
  <p>I'm not sure where the problem is here. The Rails app is running locally on port 3000 so it is not a network issue. I wonder if the test is timing out because the API takes longer to respond than Mirage - although this does seem unlikely as the tests run in under a second. Has anyone encountered a problem like this? </p>
  
  <p>Thanks</p>