Assert the mobile menu is (or is not) open. The state is the class the template puts on the page body (header--menu-open on 7.1, is-mobile-overlay-active on 7.0).
Examples
Then the mobile menu should be open
And the mobile menu should be open
Then the mobile navigation menu should be open
But the mobile menu should not be open
Then the mobile navigation menu should not be open
Pattern
Then(/^(?:the )?mobile (?:navigation )?menu should( not)* be open$/, …)
Part of @webship-js/squarespace-steps (github.com/webship/squarespace-steps), a step pack for Webship-js 2.0.x.