Then I should be logged in

Assert the session is, or is not, authenticated: the user-logged-in body class, drupalSettings.user.uid or a logout link on the page, and when a theme shows none of them, the site's own answer (an authenticated visitor is redirected away from /user/login). The negative form is what confirms a logout actually destroyed the session rather than merely redirecting.

Examples

Then I should be logged in
And we should be signed in
Then should be authenticated
And I should not be logged in
Then we should not be authenticated

Pattern

Then(/^(I |we )*should( not)* be (?:logged in|signed in|authenticated)$/, …)

Part of @webship-js/drupal-core-steps (github.com/webship/drupal-core-steps), a step pack for Webship-js 2.0.x.