Send the sign-in form of the back office with an e-mail address and a password, without expecting it to succeed: for the refused sign-in.
Examples
When I log in to the back office with "admin@example.com" and "wrong-password"
When we log in to the back office with "admin@example.com" and "wrong-password"
When I log in to the back office with "nobody@example.com" and "Whatever123456789!"
And I log in to the back office with "salesman@example.com" and "x"
When log in to the back office with "admin@example.com" and "nope"
Pattern
When(/^(I |we )*log in to the back office with "([^"]*)" and "([^"]*)"$/, …)
Part of @webship-js/prestashop-steps (github.com/webship/prestashop-steps), a step pack for Webship-js 2.0.x.