Hi Larsen,
Marketing is licensed per organisation/teanant compared with CE, it has a seperate instance.
In old july license guide, it has stated that you could receive a included(no charge) marketing application if your Dynamics 365 Customer Engagement Plan has at least 10 full users.
https://mbs.microsoft.com/Files/public/365/Dynamics365LicensingGuide.pdf
However, in November version, "no charge" and "included" keywords has been removed from Marketing license part.
https://go.microsoft.com/fwlink/?LinkId=866544&clcid=0x4809
So it could be said that you could just pay at a lower price to access marketing application even if you had 10+ users inside your action pack(in CE plan) at present,
and I thought there was no other plan to license for test than 30 days.
Regards,
Clofly