Assert the browser holds (or does not hold) the session cookie of the site: SESS or, over HTTPS, SSESS followed by a hash.
Examples
Then I should have a session cookie
Then I should not have a session cookie
And we should have a session cookie
Then we should not have a session cookie
And I should have a session cookie
Pattern
Then(/^(I |we )*should( not)* have a session cookie$/, …)
Part of @webship-js/backdrop-cms-steps (github.com/webship/backdrop-cms-steps), a step pack for Webship-js 2.0.x.