Custom Post Type testimonials can have categories settled.

Categories can be added and settled on each testimonial when editing it:

Taxonomy_-_testimonials1

And in separate tabs under Testimonials:

Taxonomy_-_testimonials2

 

You can implement such actions with Categories: add/edit name, slug, description and manage the hierarchy level. For instance, "post" category refers to parent "blog" category. Various notional connections can be emphasized in a such way:

TagsCategoriesTypes3
Testimonial categories can be found in settings of Post Types shortcode:

Taxonomy_-_posts2

Taxonomy_-_testimonials3

See more about Taxomony for Projects here - click to proceed,

for Posts - here.