Ember Acceptance testing: check that button isEnabled

I'm new to ember in general and trying to check (in my Acceptance test), whether a submit button is enabled after entering a valid email. I tried:

test('Typing email enables button', function(assert){
  visit('/');
  var theBtn = find('.btn-primary');
  fillIn('.ember-text-field', 'user@userfakemail.com');
  andThen(function(){ 
    assert.equal(theBtn.isEnabled(), true);
  });
});

But this doesn't work. And in the guides I could not find what methods were possible with find().