--- a/ChangeLog	Sat Feb 17 09:55:43 2018 +0100
+++ b/ChangeLog	Sat Feb 17 10:05:01 2018 +0100
@@ -1,3 +1,10 @@
+2018-02-17  Bruno Haible  <bruno@clisp.org>
+
+	lock: Add test of gl_once.
+	* tests/test-once.c: New file.
+	* modules/lock-tests (Files): Add it.
+	(Makefile.am): Build and test programs 'test-once1' and 'test-once2'.
+
 2018-02-17  Bruno Haible  <bruno@clisp.org>
 
 	thread: Fix compilation error on IRIX.

--- a/modules/lock-tests	Sat Feb 17 09:55:43 2018 +0100
+++ b/modules/lock-tests	Sat Feb 17 10:05:01 2018 +0100
@@ -1,6 +1,7 @@
 Files:
 tests/test-rwlock1.c
 tests/test-lock.c
+tests/test-once.c
 
 Depends-on:
 thread
@@ -11,7 +12,11 @@
 AC_CHECK_HEADERS_ONCE([semaphore.h])
 
 Makefile.am:
-TESTS += test-rwlock1 test-lock
-check_PROGRAMS += test-rwlock1 test-lock
+TESTS += test-rwlock1 test-lock test-once1 test-once2
+check_PROGRAMS += test-rwlock1 test-lock test-once1 test-once2
 test_rwlock1_LDADD = $(LDADD) @LIBMULTITHREAD@ @YIELD_LIB@
 test_lock_LDADD = $(LDADD) @LIBMULTITHREAD@ @YIELD_LIB@
+test_once1_SOURCES = test-once.c
+test_once1_LDADD = $(LDADD) @LIBTHREAD@
+test_once2_SOURCES = test-once.c
+test_once2_LDADD = $(LDADD) @LIBMULTITHREAD@

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/tests/test-once.c	Sat Feb 17 10:05:01 2018 +0100
@@ -0,0 +1,43 @@
+/* Test of once-only execution in multithreaded situations.
+   Copyright (C) 2018 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>, 2018.  */
+
+#include <config.h>
+
+#include "glthread/lock.h"
+
+#include "macros.h"
+
+gl_once_define(static, a_once)
+
+static int a;
+
+static void
+a_init (void)
+{
+  a = 42;
+}
+
+int
+main ()
+{
+  gl_once (a_once, a_init);
+
+  ASSERT (a == 42);
+
+  return 0;
+}