I believe this is tested.  In the method:

```
    def assert_data_renders_to(self, data, table):
        self.formatter(Object(name='OperationName', can_paginate=False),
                              data, self.stream)
        rendered = self.stream.getvalue()
```

that last `self.stream` is a `six.StringIO` instead which is passed as the `stream` arg (though it's positional, not a kwarg, so it's not obvious).