'Makes a request to xblock preview handler'

def _get_preview(self, usage_key, data=None):

    preview_url = reverse_usage_url('xblock_view_handler', usage_key, {'view_name': 'container_preview'})
    data = (data if data else {})
    resp = self.client.get(preview_url, data, HTTP_ACCEPT='application/json')
    return resp
