There are 2 test email options within the dashboard and it is important to note that they have different functionalities.
Send Test from Preview Page
A test email from the Preview page includes upcoming articles, specifically Boosted and Super Boosted articles, in addition to all of your Design selections. This will be the most accurate depiction of how your next newsletter will appear. Keep in mind, the AI will choose a different selection and ordering of articles (unless Boosted) from the Upcoming page for each person so you can use the drop-down menu to see examples of possible variations!
Send Test from Design Page
A test email from the tab on the Design page will only show the manually curated design elements of your newsletter template. This includes: Fonts, Colors, Images and Text, Article Settings and any other settings reflected in the Design tabs. The articles used in the test email are either stock content (if no articles have been added) OR they are selected at random and will not always mirror what is in the Upcoming page. This feature is intended to help you visualize how your Design selections will render in an actual email. For an accurate depiction of what articles will appear in your next newsletter, you'll want to refer to the Preview page.