[Config] Making tests pass on mac os x

without this change tests would fail under mac os x (at least in 10.8.2).

I think this change also removes inconstancy in the test (the `realpath()` is added in the other tests as well!).

| Q             | A
| ------------- | ---
| Bug fix?      | yes (fixes the test)
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | ~
| License       | MIT
| Doc PR        | ~


Cheers,

Christian