Posts the current digest, headed "Test send", now, without moving the schedule. With no body it goes to the saved Slack channels and email addresses, at most once per 10 minutes per team, and a team with no saved destination is a 400. With a body it goes only to the body's slackConfigurationIds and emailAddresses, validated as on save (this team's Slack connections, at most 5; at most 20 valid addresses), and nothing is saved. Every test is allowed at most once per 10 minutes per team; a body test emailing anyone who is not a user in your account and not on a company domain of its users (public mail domains never count) is also allowed at most once per 10 minutes across all teams of your account. Admins only. A test inside its window is a 429.