Index: head/etc/mtree/BSD.tests.dist
===================================================================
--- head/etc/mtree/BSD.tests.dist
+++ head/etc/mtree/BSD.tests.dist
@@ -440,6 +440,8 @@
             files
             ..
         ..
+        ping
+        ..
     ..
     secure
         lib
Index: head/sbin/ping/Makefile
===================================================================
--- head/sbin/ping/Makefile
+++ head/sbin/ping/Makefile
@@ -23,4 +23,7 @@
 CFLAGS+=-DIPSEC
 LIBADD+=	ipsec
 
+HAS_TESTS=
+SUBDIR.${MK_TESTS}+= tests
+
 .include <bsd.prog.mk>
Index: head/sbin/ping/tests/Makefile
===================================================================
--- head/sbin/ping/tests/Makefile
+++ head/sbin/ping/tests/Makefile
@@ -0,0 +1,8 @@
+# $FreeBSD$
+
+WARNS?=	6
+
+ATF_TESTS_C+=	in_cksum_test
+SRCS.in_cksum_test= in_cksum_test.c ../utils.c
+
+.include <bsd.test.mk>
Index: head/sbin/ping/tests/in_cksum_test.c
===================================================================
--- head/sbin/ping/tests/in_cksum_test.c
+++ head/sbin/ping/tests/in_cksum_test.c
@@ -0,0 +1,146 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
+ *
+ * Copyright (C) 2019 Jan Sucan <jansucan@FreeBSD.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <sys/param.h>
+
+#include <atf-c.h>
+
+#include "../utils.h"
+
+/*
+ * Test cases.
+ */
+
+ATF_TC_WITHOUT_HEAD(aligned_even_length_big_endian);
+ATF_TC_BODY(aligned_even_length_big_endian, tc)
+{
+	u_char data[] __aligned(sizeof(u_short)) =
+		{0x12, 0x34, 0x56, 0x78};
+	u_short sum;
+
+	sum = in_cksum(data, nitems(data));
+	ATF_REQUIRE(sum == 0x5397);
+}
+
+ATF_TC_WITHOUT_HEAD(aligned_odd_length_big_endian);
+ATF_TC_BODY(aligned_odd_length_big_endian, tc)
+{
+	u_char data[] __aligned(sizeof(u_short)) =
+		{0x12, 0x34, 0x56, 0x78, 0x9a};
+	u_short sum;
+
+	sum = in_cksum(data, nitems(data));
+	ATF_REQUIRE(sum == 0x52fd);
+}
+
+ATF_TC_WITHOUT_HEAD(aligned_even_length_little_endian);
+ATF_TC_BODY(aligned_even_length_little_endian, tc)
+{
+	u_char data[] __aligned(sizeof(u_short)) =
+		{0x34, 0x12, 0x78, 0x56};
+	u_short sum;
+
+	sum = in_cksum(data, nitems(data));
+	ATF_REQUIRE_MSG(sum == 0x9753, "%d", sum);
+}
+
+ATF_TC_WITHOUT_HEAD(aligned_odd_length_little_endian);
+ATF_TC_BODY(aligned_odd_length_little_endian, tc)
+{
+	u_char data[] __aligned(sizeof(u_short)) =
+		{0x34, 0x12, 0x78, 0x56, 0x00, 0x9a};
+	u_short sum;
+
+	sum = in_cksum(data, nitems(data));
+	ATF_REQUIRE(sum == 0xfd52);
+}
+
+ATF_TC_WITHOUT_HEAD(unaligned_even_length_big_endian);
+ATF_TC_BODY(unaligned_even_length_big_endian, tc)
+{
+	u_char data[] __aligned(sizeof(u_short)) =
+		{0x00, 0x12, 0x34, 0x56, 0x78};
+	u_short sum;
+
+	sum = in_cksum(data + 1, nitems(data) - 1);
+	ATF_REQUIRE(sum == 0x5397);
+}
+
+ATF_TC_WITHOUT_HEAD(unaligned_odd_length_big_endian);
+ATF_TC_BODY(unaligned_odd_length_big_endian, tc)
+{
+	u_char data[] __aligned(sizeof(u_short)) =
+		{0x00, 0x12, 0x34, 0x56, 0x78, 0x9a};
+	u_short sum;
+
+	sum = in_cksum(data + 1, nitems(data) - 1);
+	ATF_REQUIRE(sum == 0x52fd);
+}
+
+ATF_TC_WITHOUT_HEAD(unaligned_even_length_little_endian);
+ATF_TC_BODY(unaligned_even_length_little_endian, tc)
+{
+	u_char data[] __aligned(sizeof(u_short)) =
+		{0x00, 0x34, 0x12, 0x78, 0x56};
+	u_short sum;
+
+	sum = in_cksum(data + 1, nitems(data) - 1);
+	ATF_REQUIRE_MSG(sum == 0x9753, "%d", sum);
+}
+
+ATF_TC_WITHOUT_HEAD(unaligned_odd_length_little_endian);
+ATF_TC_BODY(unaligned_odd_length_little_endian, tc)
+{
+	u_char data[] __aligned(sizeof(u_short)) =
+		{0x00, 0x34, 0x12, 0x78, 0x56, 0x00, 0x9a};
+	u_short sum;
+
+	sum = in_cksum(data + 1, nitems(data) - 1);
+	ATF_REQUIRE(sum == 0xfd52);
+}
+
+/*
+ * Main.
+ */
+
+ATF_TP_ADD_TCS(tp)
+{
+	ATF_TP_ADD_TC(tp, aligned_even_length_big_endian);
+	ATF_TP_ADD_TC(tp, aligned_odd_length_big_endian);
+	ATF_TP_ADD_TC(tp, aligned_even_length_little_endian);
+	ATF_TP_ADD_TC(tp, aligned_odd_length_little_endian);
+	ATF_TP_ADD_TC(tp, unaligned_even_length_big_endian);
+	ATF_TP_ADD_TC(tp, unaligned_odd_length_big_endian);
+	ATF_TP_ADD_TC(tp, unaligned_even_length_little_endian);
+	ATF_TP_ADD_TC(tp, unaligned_odd_length_little_endian);
+
+	return (atf_no_error());
+}