Ok I see what you're doing now. Could you please setup your stubs inside the `setup` function so that the body of the test function is not so cluttered with setup work. Suggest something like:

```js
this.app.storage = sinon.createStubInstance(this.Storage);
this.app.storage.image = { delete: sinon.stub(), ... };
this.app.storage.video = { delete: sinon.stub(), ... };
```