'Test preferred compilers are applied correctly'

def test_preferred_compilers(self, refresh_builtin_mock):

    update_packages('mpileaks', 'compiler', ['clang@3.3'])
    spec = concretize('mpileaks')
    assert (spec.compiler == spack.spec.CompilerSpec('clang@3.3'))
    update_packages('mpileaks', 'compiler', ['gcc@4.5.0'])
    spec = concretize('mpileaks')
    assert (spec.compiler == spack.spec.CompilerSpec('gcc@4.5.0'))
