Log out of the backend through the user menu of the toolbar (.toolbar-item-user, the "Logout" button) and wait for the login form.
Examples
When I log out
When we log out
And I log out of the backend
When I sign out
When log out of the backend
Pattern
When(/^(I |we )*(?:log ?out|sign out)(?: of the backend)?$/, …)
Part of @webship-js/typo3-steps (github.com/webship/typo3-steps), a step pack for Webship-js 2.0.x.