Your expectation is simply wrong.  dirname() is documented to return the directory component of a pathname you feed it.  You fed it /test.php and it gave you back / (or the Windows equivalent thereof) as expected.`

That reasoning doesn't quite go along with what the documentation says, IMHO:

(quoted from http://www.php.net/dirname)
"[...]Essentially, this means that if there are no slashes in path , a dot ('.') is returned, indicating the current directory. Otherwise, the returned string is path with any trailing /component removed.[...]"

So for the input '/test.php', the first case (no slashes in path) obviously doesn't apply, since there is a slash contained in the path in question.

Now, the second case states that the returned string is the path ('/test.php') with any trailing /component (in this case '/test.php') removed, i.e. simply ''.

So there seems to be some kind of contradiction between the manual and what you said, could your elaborate on that, please? Apologies if I'm missing the point,

Michael

PS: Even if the behaviour was changed to return '/' instead of an empty string, the transformation of '/' to the default directory separator should still be officially documented (and not in the user comments).

No, the trailing / the docs talk about are cases where you actually have a trailing / in the source path.  eg. /some/path/
It does not mean that the trailing path of the returned string will be stripped.

See also:
http://bugs.php.net/bug.php?id=20895

Maybe someone with a clue (unlike me) can document this.