Assert the admin bar, the toolbar on top of the site and of the dashboard, has, or does not have, an item. For a visitor who may edit, it offers "Edit Post" or "Edit Page" on the entry being viewed.
Examples
Then the admin bar should list "Edit Post"
And the admin bar should list "New"
Then the admin bar should not list "Edit Page"
And the admin bar should list "Dashboard"
Then the admin bar should not list "Customize"
Pattern
Then(/^the admin bar should( not)* list "([^"]*)"$/, …)
Part of @webship-js/wordpress-steps (github.com/webship/wordpress-steps), a step pack for Webship-js 2.0.x.