How to get dune to generate a .merlin file for a library that is not public

Ecosystem
1

I have a src/ directory with a dune file describing a public library. There is a generated .merlin file in that directory.

I have a test/ directory with a dune file desrcribing a non-public library. There is no generated .merlin file in that directory.

My question is: how to get a dune-generated .merlin file in the test/ directory?

2

Please ignore this question. The .merlin gets generated when I try to build e.g. something that depends on the non-public library.