Assert the error a form shows under one of its fields, in the back office (a red line under the field) or in the shop.
Examples
Then I should see the field error "The field name is required at least in your default language."
Then I should see the field error "This value should be either positive or zero."
Then we should see the field error "This voucher does not exist."
And I should not see the field error "The field name is required"
Then I should see the field error "is required"
Pattern
Then(/^(I |we )*should( not)* see the field error "([^"]*)"$/, …)
Part of @webship-js/prestashop-steps (github.com/webship/prestashop-steps), a step pack for Webship-js 2.0.x.