Assert the top bar offers, or does not offer, a page action by its text: the primary action ("Edit") or one of the dropdown's entries ("Delete", "Revisions", "Duplicate"), which are in the markup whether or not the dropdown is open.
Examples
Then the top bar should offer the "Edit" action
And the top bar should offer the "Delete" action
Then the top bar should offer the "Revisions" action
And the top bar should not offer the "Delete" action
Then the top bar should not offer the "Edit layout" action
Pattern
Then(/^the top bar should( not)* offer the "([^"]*)" action$/, …)
Part of @webship-js/drupal-core-steps (github.com/webship/drupal-core-steps), a step pack for Webship-js 2.0.x.