Follow instructions as per https://phabricator.wikimedia.org/T183817 to mock an API edit
On success, make sure Nesletter:Foobar is:
- Created and saved in database and have the data as expected (description, mainpage)
- Page Newsletter:Foobar exists and have the data as expected (description, mainpage)
- User UserName is a publisher and subscribed to Newsletter Foobar.