Add obj=obj to get it in failing assert messages
Adding obj=obj in this call to assert_attr_equal helps make failing test cases more easily debuggable. This follows the pattern elsewhere in this same file of other calls to assert_attr_equal and related methods.

- [ ] closes #xxxx
- [ ] tests added / passed
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry
