Assert the list on the page is empty: Joomla shows its "No Matching Results" notice instead of rows (or, with "not", that the list has rows).
Examples
Then I should see an empty list
Then I should not see an empty list
Then we should see an empty list
And I should not see an empty list
Then should see an empty list
Pattern
Then(/^(I |we )*should( not)* see an empty list$/, …)
Part of @webship-js/joomla-steps (github.com/webship/joomla-steps), a step pack for Webship-js 2.0.x.