Assert the consent manager stored, or did not store, an answer for the visitor at all: after "Accept", "Decline" or a saved selection one is stored and the notice stays away; before that, none is.
Examples
Then the cookie consent should be stored
And the cookie consent should be stored
Then the cookie consent should not be stored
And the cookie consent should not be stored
Then the visitor's cookie consent should be stored
Pattern
Then(/^the (?:visitor's )?cookie consent should( not)* be stored$/, …)
Part of @webship-js/drupal-cms-steps (github.com/webship/drupal-cms-steps), a step pack for Webship-js 2.0.x.