Assert the browser refused to submit the form because a required field is empty, naming the field: HTML5 constraint validation blocks the submit before any request is made, and the form stays on screen.
Examples
Then the "Title" field should block submission as required
And the "Description" field should block submission as required
Then the "Content" field should block submission as required
And the "SEO title" field should block submission as required
Then the "Name" field should block submission as required
Pattern
Then(/^the "([^"]*)" field should block submission as required$/, …)
Part of @webship-js/drupal-core-steps (github.com/webship/drupal-core-steps), a step pack for Webship-js 2.0.x.