Assert the Navigation module's admin sidebar (#admin-toolbar) is, or is not, present.
The counterpart to the toolbar step above, for the newer of the two admin UIs; they target different markup, so neither replaces the other. The negative form is the one that proves a logout really dropped the session's admin privileges rather than just redirecting.
Examples
Then I should see the navigation sidebar
And we should see the admin navigation sidebar
Then should see the navigation sidebar
And I should not see the navigation sidebar
Then we should not see the admin navigation sidebar
Pattern
Then(/^(I |we )*should( not)* see the (?:admin )?navigation sidebar$/, …)
Part of @webship-js/drupal-core-steps (github.com/webship/drupal-core-steps), a step pack for Webship-js 2.0.x.