Desired Behavior

Cram tests (and (system ...) commands) run in the default system shell. It would be useful to be able to specify a specific shell to use instead.

My specific use case is that I want to guarantee portability while writing tests, but I don't want to assume compatibility with my system shell (on MacOS, usually). Being able to automatically use a shell like dash would be an easy way to catch non-portable commands.

Example

I think it would make sense to expose this option as an environment variable or a CLI flag, since the configuration is local and I probably don't want to commit it in a dune file.

 DUNE_SHELL=/usr/local/bin/dash dune runtest

or

dune runtest --shell=/usr/local/bin/dash