Make sure the session is anonymous: drop the cookies of the browser, open /typo3/ and confirm the login form is shown.
Examples
Given I am not logged in
Given we are not logged in
Given not logged in
And I am not logged in
But I am not logged in
Pattern
Given(/^(I am |we are )*not logged in$/, …)
Part of @webship-js/typo3-steps (github.com/webship/typo3-steps), a step pack for Webship-js 2.0.x.