'Verify that virtuals are not allowed in packages.yaml.'

def test_no_virtuals_in_packages_yaml(self):

    conf = syaml.load('mpi:\n                paths:\n                        mpi-with-lapack@2.1:    /path/to/lapack\n')
    spack.config.update_config('packages', conf, 'concretize')
    with pytest.raises(spack.package_prefs.VirtualInPackagesYAMLError):
        spack.package_prefs.get_packages_config()
