I'm trying to make https://github.com/haampie/spack-batteries-included pass its tests, which currently fail because spack is mounted on an immutable filesystem and multiple tests try to write to the <spack>/opt folder.

Steps to reproduce the issue

$ wget https://github.com/haampie/spack-batteries-included/releases/download/v1.0.0/spack.x
$ chmod +x spack.x
$ ./spack.x unit-test -o cache_dir=$PWD/.cache -k develop

All tests fail, except when I add mutable_database to all.