Assert the local tasks, the tab strip core builds from a module's *.links.task.yml, are or are not present: the navigation core labels with primary-tabs-title, or the .tabs classes of core's themes; the "local tasks" named selector overrides both.
Examples
Then I should see the local tasks
And we should see the tabs
Then should see the primary tabs
And I should see the local tasks
Then we should not see the local tasks
Pattern
Then(/^(I |we )*should( not)* see the (?:primary )?(?:local tasks|tabs)$/, …)
Part of @webship-js/drupal-cms-steps (github.com/webship/drupal-cms-steps), a step pack for Webship-js 2.0.x.