Assert the admin list on the page has (or does not have) a row named exactly so: a username in the users list, a group name in the groups list.
Examples
Then I should see "editor" in the admin list
Then I should not see "nobody" in the admin list
And we should see "Editors" in the admin list
Then should see "admin" in the admin list
But we should not see "Publishers" in the admin list
Pattern
Then(/^(I |we )*should( not)* see "([^"]*)" in the admin list$/, …)
Part of @webship-js/django-cms-steps (github.com/webship/django-cms-steps), a step pack for Webship-js 2.0.x.