Press a button of the administrator toolbar by its text ("New", "Save", "Save & Close", "Cancel", "Publish", "Trash", "Check-in", ...). Buttons inside the "Actions" dropdown are reached by opening it first. A disabled button (a list action with no row selected) fails with a hint.
Examples
When I click the "New" toolbar button
When I click the "Save & Close" toolbar button
When we click the "Cancel" toolbar button
And I click the "Publish" toolbar button
When click the "Trash" toolbar button
Pattern
When(/^(I |we )*click the "([^"]*)?" toolbar button$/, …)
Part of @webship-js/joomla-steps (github.com/webship/joomla-steps), a step pack for Webship-js 2.0.x.