Apply specific 'using' syntax to the tests

[clizbe]

Description

We decided to be explicit with our using so that we can always see what package provides a function.
We changed it for src, but need to apply it to test.

Here's the Issue and PR from applying it to src for reference:

• Apply specific "using" syntax #431
• Don't use unqualified using and update README.dev.md with guidelines #533

Validation and testing

Rerun tests

Motivation

Save future devs!

Target audience

devs

Can you help?

Yes