Assert the admin login form shows (or does not show) its error note (.errornote), optionally with a text it must contain.
Examples
Then I should see a login error
Then I should not see a login error
And we should see a login error "Please enter the correct username and password"
Then should see the login error "staff account"
But I should not see a login error "inactive"
Pattern
Then(/^(I |we )*should( not)* see (?:a|the) login error(?: "([^"]*)")?$/, …)
Part of @webship-js/django-cms-steps (github.com/webship/django-cms-steps), a step pack for Webship-js 2.0.x.