Unpublish the page being viewed, through "Manage Versions" in the toolbar's "Version" menu: the versions list opens in the CMS sideframe, where the step chooses "Unpublish" for the published version and confirms.
Examples
When I unpublish the page
When we unpublish the page
And I unpublish the page
When unpublish the page
And we unpublish the page
Pattern
When(/^(I |we )*unpublish the page$/, …)
Part of @webship-js/django-cms-steps (github.com/webship/django-cms-steps), a step pack for Webship-js 2.0.x.