Then the default theme should be "Olivero"

Assert which theme is the site's default theme, by the name the Appearance page (/admin/appearance) shows next to "(default theme)", or next to "(default theme, administration theme)" when one theme serves as both.

Examples

Then the default theme should be "Olivero"
And the default theme should be "Mercury"
Then the default theme should not be "Bartik"
And the default theme should be "Claro"
Then the default theme should not be "Stark"

Pattern

Then(/^the default theme should( not)* be "([^"]*)"$/, …)

Part of @webship-js/drupal-cms-steps (github.com/webship/drupal-cms-steps), a step pack for Webship-js 2.0.x.