On 16 Aug 2017, at 09:42, Sean McBride <sean@...> wrote:

You could presumably test it in a VM, or using a spare old external drive or USB key, or even just create a disk image.  You don't need an extra Mac whose boot disk can be wiped.

You do if you want to test APFS, which is only available for SSD or Fusion disks the last time I checked. 

Admittedly, I haven’t yet checked the release notes for the most recent beta, but I've been having problems getting previous betas of HS to install on Parallels anyway. 

I was able to make a disk image with APFS format, and it wasn't in the latest beta.  I didn't try making an APFS boot disk, which you might need for some kinds of testing.