Send a message on the record with the "Send message" button of the chatter, and wait for the message to appear in the thread. A message is sent to the followers of the record: on a test site, make sure outgoing mail is not delivered to real addresses.
Examples
When I send the message "Your order is confirmed"
When we send the message "Thank you for your request"
And I send the message "The quotation is attached"
When I send the chatter message "We will call you back"
And we send the chatter message "Delivery is planned"
Pattern
When(/^(I |we )*send the (?:chatter )?message "([^"]*)"$/, …)
Part of @webship-js/odoo-steps (github.com/webship/odoo-steps), a step pack for Webship-js 2.0.x.