dirfd: Add tests.

* tests/test-dirfd.c: New file.
* modules/dirfd-tests: New file.

3 files changed, 64 insertions, 0 deletions

diff --git a/ChangeLog b/ChangeLog
index 5f01a52535..06ff163e0e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,11 @@
 2023-05-05  Bruno Haible  <bruno@clisp.org>
 
+	dirfd: Add tests.
+	* tests/test-dirfd.c: New file.
+	* modules/dirfd-tests: New file.
+
+2023-05-05  Bruno Haible  <bruno@clisp.org>
+
 	dirfd: Fix bogus override (regression 2023-04-26).
 	Reported by Bjarni Ingi Gislason <bjarniig@simnet.is> in
 	<https://lists.gnu.org/archive/html/bug-gnulib/2023-05/msg00040.html>.
diff --git a/modules/dirfd-tests b/modules/dirfd-tests
new file mode 100644
index 0000000000..0738351042
--- /dev/null
+++ b/modules/dirfd-tests
@@ -0,0 +1,11 @@
+Files:
+tests/test-dirfd.c
+tests/macros.h
+
+Depends-on:
+
+configure.ac:
+
+Makefile.am:
+TESTS += test-dirfd
+check_PROGRAMS += test-dirfd
diff --git a/tests/test-dirfd.c b/tests/test-dirfd.c
new file mode 100644
index 0000000000..f7fd395a9c
--- /dev/null
+++ b/tests/test-dirfd.c
@@ -0,0 +1,47 @@
+/* Test of dirfd() function.
+   Copyright (C) 2023 Free Software Foundation, Inc.
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
+
+/* Written by Bruno Haible <bruno@clisp.org>, 2023.  */
+
+#include <config.h>
+
+#include <dirent.h>
+
+#include <stdio.h>
+
+#include "macros.h"
+
+int
+main ()
+{
+#if defined _WIN32 && !defined __CYGWIN__
+  fprintf (stderr, "Skipping test: The DIR type does not contain a file descriptor.\n");
+  return 77;
+#else
+  /* On all other platforms, we expect to have either
+       - a dirfd() function, or
+       - a dirfd macro, or
+       - a DIR struct with a d_fd member, or
+       - a DIR struct with a dd_fd member.
+     If we don't have this, dirfd.c produces a function that always returns -1.
+     Check here that this does not happen.  */
+  DIR *d = opendir (".");
+  int fd = dirfd (d);
+  ASSERT (fd >= 0);
+
+  return 0;
+#endif
+}