This fixes some errors with setting up test configuration. These
errors do not cause current Spack tests to fail but do create
red herring issues elsewhere (see #15666). Fixing these errors
leads to more errors in tests that depended on the original
misconfigured state, so those are also addressed here.
This is an update to #16003 which accounts for some unit tests with
conflicting config/mutable_config fixtures. These conflicts were
not exposed until the mutable_config fixture was fixed. Details are
included below. The change which builds on #16003 is prefixed with
"(new)".
* For tests that use the real Spack package repository, the config
needs to avoid using MPI providers that are not intended to be
installed by Spack. Without this, it is possible that Spack tests
which concretize the MPI virtual will end up trying to use an
implementation that it shouldn't (e.g. one that is always
provided externally). See #15666 for an example.
* The mutable_config test fixture was not initializing the scope
roots to the right directories (so the resulting config was empty).
* The current_host fixture in the concretize.py tests was using the
config fixture rather than mutable_config, and was polluting the
config cache for other tests.
* One test in concretize.py was clearing a nonexistent cache
(PackagePrefs._packages_config_cache). This reference has been
removed.
* The test 'test_preferred_compilers' was was depending on cross
test config pollution to succeed. The initial spec before
concretization has been updated to updated to be explicit about
the desired result.
* (new) For tests that use install_mockery and mutable_config,
replace install_mockery with a separate install_mockery_mutable_config
fixture that is exactly the same as install_mockery but uses the
mutable_config fixture to avoid conflicts.
1ed564a1e6