fdopendir-tests: test it does not close its arg

* tests/test-fdopendir.c (main): Test that fdopendir does not
close its argument.  From a suggestion by David Grayson in:
http://lists.gnu.org/archive/html/bug-gnulib/2015-03/msg00039.html

1 files changed, 8 insertions, 4 deletions

diff --git a/tests/test-fdopendir.c b/tests/test-fdopendir.c
index 1afbf9db39..8fd43824e9 100644
--- a/tests/test-fdopendir.c
+++ b/tests/test-fdopendir.c
@@ -64,11 +64,15 @@ main (int argc _GL_UNUSED, char *argv[])
   fd = open (".", O_RDONLY);
   ASSERT (0 <= fd);
   d = fdopendir (fd);
-  /* We know that fd is now out of our reach, but it is not specified
-     whether it is closed now or at the closedir.  We also can't
-     guarantee whether dirfd returns fd, some other descriptor, or
-     -1.  */
   ASSERT (d);
+  /* fdopendir should not close fd.  */
+  ASSERT (dup2 (fd, fd) == fd);
+
+  /* Don't test dirfd here.  dirfd (d) must return fd on current POSIX
+     platforms, but on pre-2008 platforms or on non-POSIX platforms
+     dirfd (fd) might return some other descriptor, or -1, and gnulib
+     does not work around this porting problem.  */
+
   ASSERT (closedir (d) == 0);
   /* Now we can guarantee that fd must be closed.  */
   errno = 0;