Resolve "Allow mini files in unit tests"

What does this MR do?

Implements a solution for #105 (closed).

A way to test this is actually moving the test of parametrization to dune/dorie/test.

Is there something that needs to be double checked?

Can this MR be accepted?

• Implemented
• Added test
• Pipeline passing
• Added entry to CHANGELOG.md

Related issues

Closes #105 (closed)