If you have a reference field in your Testimonials that link to your Location collection. Within each testimonial you can select which location you want to attach it to.
Then from the Locations template when you add the CMS element link it to Testimonials. Open the options menu (Cog Icon) and go to filters.
The first dropdown you select Locations the second should auto complete to Equals and the third should be Current Locations.
After that you good to go, only the testimonials that you have linked to that location will show on that location page.
Hope it helps,
EDIT: I just did this up for someone else relating to a gallery CMS linking to a guests CMS. Same principles so heres a video example that explains.