Assert the screen shows, or does not show, an administration notice of a kind, optionally containing a text. Notices are what a screen answers after an action: "Settings saved.", "Plugin activated.", "1 post moved to the Trash.". The kinds are success, error, warning and info.
Examples
Then I should see a success notice
And we should see a success notice "Settings saved."
Then I should see an error notice "could not"
And I should not see an error notice
But we should not see a warning notice "Update"
Pattern
Then(/^(I |we )*should( not)* see an? (success|error|warning|info) notice(?: "([^"]*)")?$/, …)
Part of @webship-js/wordpress-steps (github.com/webship/wordpress-steps), a step pack for Webship-js 2.0.x.