Assert the active theme is a block theme (with the Site Editor and block templates) or a classic theme (with PHP templates, widget areas and menus). It asks the REST API, as an administrator. It tells which screens exist: Appearance > Editor and Navigation for a block theme, Widgets and Menus for a classic theme.
Examples
Then the active theme should be a block theme
And the active theme should be a block theme
Then the active theme should not be a classic theme
And the active theme should be a classic theme
Then the active theme should not be a block theme
Pattern
Then(/^the active theme should( not)* be a (block|classic) theme$/, …)
Part of @webship-js/wordpress-steps (github.com/webship/wordpress-steps), a step pack for Webship-js 2.0.x.