Some of our tags, such as <optionalBlock> and <dropdownList> involves grouping of sibling table rows, and controlling visibility of them. So when such tags nest to each other, the visibility updates need to be done carefully, or else the visibility could get out of sync with the model (imagine outer group is made visible while inner group is not visible --- if all the rows are simply enumerated and visibility changed, we end up making the inner group visible.)

The rowVisibilityGroup object in hudson-behavior.js is used to coordinate this activity, and this test ensures that it's working.