Assert the admin toolbar is rendered — the cheapest signal that the session is (or is not) authenticated.
Examples
Then I should see the admin bar
And we should see the admin toolbar
Then should see the toolbar
Then I should not see the admin bar
But we should not see the toolbar
Pattern
Then(/^(I |we )*should( not)* see the (?:admin (?:bar|toolbar)|toolbar)$/, …)
Part of @webship-js/wordpress-steps (github.com/webship/wordpress-steps), a step pack for Webship-js 2.0.x.