Here is the link to start a free Office 365 trial (Enterprise E3 version – not that this is not for the home version of Office 365).
https://products.office.com/en-us/business/office-365-enterprise-e3-business-software (or http://aka.ms/jsn2ec). I use this whenever I set up a new tenant for testing purposes.
Note that once started, you can extend this for another 30 days, if it is within 15 days of expiring. Make sure you set a reminder, because once it has expired you cannot extend the trial (unless you ask support very nicely!).
Also, once your E3 (plus extension) has finished, you can start an E5 trial, and then extend that. Then you can start a Business Essentials trial, and so on.
