Assert a message of a type contains (or equals) a text, or that no message of that type does. The types are the ones the site renders: status, info, warning and error.
Examples
Then the status message should contain "has been created"
Then the error message should be "Title field is required."
And the warning message should contain "unsaved changes"
Then the error message should not contain "password"
And the status message should be "The changes have been saved."
Pattern
Then(/^the (status|info|warning|error) message should( not)* (be|contain) "([^"]*)"$/, …)
Part of @webship-js/backdrop-cms-steps (github.com/webship/backdrop-cms-steps), a step pack for Webship-js 2.0.x.