--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,12 @@
 2012-01-02  Bruno Haible  <bruno@clisp.org>
 
+	Enhance tests for module 'isatty'.
+	* modules/isatty-tests (Depends-on): Add pipe-posix.
+	* tests/test-isatty.c: Include <fcntl.h>.
+	(DEV_NULL): New macro.
+	(main): Test the resut of isatty() also on regular files, pipes, and
+	/dev/null.
+
 	New module 'isatty'.
 	* lib/unistd.in.h (isatty): New declaration.
 	* lib/isatty.c: New file, based on an idea of

--- a/modules/isatty-tests
+++ b/modules/isatty-tests
@@ -5,6 +5,7 @@
 
 Depends-on:
 unistd
+pipe-posix
 
 configure.ac:
 

--- a/tests/test-isatty.c
+++ b/tests/test-isatty.c
@@ -22,12 +22,24 @@
 SIGNATURE_CHECK (isatty, int, (int));
 
 #include <errno.h>
+#include <fcntl.h>
 
 #include "macros.h"
 
+/* The name of the "always silent" device.  */
+#if (defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__
+/* Native Woe32 API.  */
+# define DEV_NULL "NUL"
+#else
+/* Unix API.  */
+# define DEV_NULL "/dev/null"
+#endif
+
 int
 main (void)
 {
+  const char *file = "test-isatty.txt";
+
   /* Test behaviour for invalid file descriptors.  */
   {
     errno = 0;
@@ -44,5 +56,43 @@
            );
   }
 
+  /* Test behaviour for regular files.  */
+  {
+    int fd;
+
+    fd = open (file, O_WRONLY|O_CREAT|O_TRUNC, 0644);
+    ASSERT (0 <= fd);
+    ASSERT (write (fd, "hello", 5) == 5);
+    ASSERT (close (fd) == 0);
+
+    fd = open (file, O_RDONLY);
+    ASSERT (0 <= fd);
+    ASSERT (! isatty (fd));
+    ASSERT (close (fd) == 0);
+  }
+
+  /* Test behaviour for pipes.  */
+  {
+    int fd[2];
+
+    ASSERT (pipe (fd) == 0);
+    ASSERT (! isatty (fd[0]));
+    ASSERT (! isatty (fd[1]));
+    ASSERT (close (fd[0]) == 0);
+    ASSERT (close (fd[1]) == 0);
+  }
+
+  /* Test behaviour for /dev/null.  */
+  {
+    int fd;
+
+    fd = open (DEV_NULL, O_RDONLY);
+    ASSERT (0 <= fd);
+    ASSERT (! isatty (fd));
+    ASSERT (close (fd) == 0);
+  }
+
+  ASSERT (unlink (file) == 0);
+
   return 0;
 }