Sent! Although I just realized it’s not like only one person has to send an e-mail; multiple would make it clearer that these images are important to some people.
https://cdimage.debian.org/cdimage/weekly-live-builds/amd64/iso-hybrid/
The files just aren't there (yet?), website probably got updated prematurely.
In case you want to install testing for personal use (not for testing the ISO), the officially recommended way is to install a minimal stable system, change the sources.list to point to testing, do a dist-upgrade and then install what packages you need.
Your options are to test Stable instead, or wait till the Testing live images are available.
Since the supported way to install Debian is always via Stable, the Testing images are really only there for devs and bug squashers to test the installer itself before it's released.