Could you test that the ResourceCollection **is in the identity map** before destroying it?

```js
describe('Given a ResourceCollection in the identity map', function() {
  beforeEach(function() {
    instance =
    ...
  });

  it('is registered in the identity map', function() {
    // expect instance to be in the identity map
  });

  describe('destroying a ResourceCollection instance', function() {
    beforeEach(function() {
      instance.destroy();
    });
    ...
```