Assert a placeholder has (or does not have) a plugin of a type, on the structure board. The step opens the board when needed.
Examples
Then the "Page Content" placeholder should have a "Text" plugin
Then the "Page Content" placeholder should not have a "Link" plugin
And the "Page Content" placeholder should contain an "Alert" plugin
Then the "Sidebar" placeholder should not contain a "Text" plugin
But the "Page Content" placeholder should not have a "Card" plugin
Pattern
Then(/^the "([^"]*)" placeholder should( not)* (?:have|contain) an? "([^"]*)" plugin$/, …)
Part of @webship-js/django-cms-steps (github.com/webship/django-cms-steps), a step pack for Webship-js 2.0.x.