Assert the current page is (or is not) the site's built-in 404 page, by its "404: Not Found" copy.
Examples
Then I should be on the default 404 page
Then we should be on the default 404 page
And I should not be on the default 404 page
Then should be on the default 404 page
And we should be on the default 404 page
Pattern
Then(/^(I |we )*should( not)* be on the default 404 page$/, …)
Part of @webship-js/gatsby-steps (github.com/webship/gatsby-steps), a step pack for Webship-js 2.0.x.