Index: tests/sys/netinet/Makefile
===================================================================
--- tests/sys/netinet/Makefile
+++ tests/sys/netinet/Makefile
@@ -10,7 +10,15 @@
 		socket_afinet \
 		tcp_connect_port_test
 
-ATF_TESTS_SH=	carp fibs fibs_test redirect divert forward output lpm arp
+ATF_TESTS_SH=	carp fibs \
+		fibs_test \
+		redirect \
+		divert \
+		forward \
+		output \
+		lpm \
+		arp \
+		if_wg_test
 TEST_METADATA.output+=	required_programs="python"
 
 PROGS=	udp_dontroute tcp_user_cookie
Index: tests/sys/netinet/if_wg_test.sh
===================================================================
--- /dev/null
+++ tests/sys/netinet/if_wg_test.sh
@@ -0,0 +1,99 @@
+# $FreeBSD$
+#
+# SPDX-License-Identifier: BSD-2-Clause-FreeBSD
+#
+# Copyright (c) 2021 The FreeBSD Foundation
+#
+# This software was developed by Mark Johnston under sponsorship
+# from the FreeBSD Foundation.
+#
+# 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.
+
+. $(atf_get_srcdir)/../common/vnet.subr
+
+atf_test_case "wg_basic" "cleanup"
+wg_basic_head()
+{
+	atf_set descr 'Create a wg(4) tunnel over an epair and pass traffic between jails'
+	atf_set require.user root
+}
+
+wg_basic_body()
+{
+	local epair pri1 pri2 pub1 pub2 wg1 wg2
+        local endpoint1 endpoint2 tunnel1 tunnel2
+
+	kldload -n if_wg
+
+	pri1=$(openssl rand -base64 32)
+	pri2=$(openssl rand -base64 32)
+
+	endpoint1=192.168.2.1
+	endpoint2=192.168.2.2
+	tunnel1=169.254.0.1
+	tunnel2=169.254.0.2
+
+	epair=$(vnet_mkepair)
+
+	vnet_init
+
+	vnet_mkjail wgtest1 ${epair}a
+	vnet_mkjail wgtest2 ${epair}b
+
+	# Workaround for PR 254212.
+	jexec wgtest1 ifconfig lo0 up
+	jexec wgtest2 ifconfig lo0 up
+
+	jexec wgtest1 ifconfig ${epair}a $endpoint1 up
+	jexec wgtest2 ifconfig ${epair}b $endpoint2 up
+
+	wg1=$(jexec wgtest1 ifconfig wg create listen-port 12345 private-key "$pri1")
+	pub1=$(jexec wgtest1 ifconfig $wg1 | awk '/public-key:/ {print $2}')
+	wg2=$(jexec wgtest2 ifconfig wg create listen-port 12345 private-key "$pri2")
+	pub2=$(jexec wgtest2 ifconfig $wg2 | awk '/public-key:/ {print $2}')
+
+	atf_check -s exit:0 -o ignore \
+	    jexec wgtest1 ifconfig $wg1 peer public-key "$pub2" \
+	    endpoint ${endpoint2}:12345 allowed-ips ${tunnel2}/32
+	atf_check -s exit:0 \
+	    jexec wgtest1 ifconfig $wg1 inet $tunnel1
+
+	atf_check -s exit:0 -o ignore \
+	    jexec wgtest2 ifconfig $wg2 peer public-key "$pub1" \
+	    endpoint ${endpoint1}:12345 allowed-ips ${tunnel1}/32
+	atf_check -s exit:0 \
+	    jexec wgtest2 ifconfig $wg2 inet $tunnel2
+
+	# Generous timeout since the handshake takes some time.
+	atf_check -s exit:0 -o ignore jexec wgtest1 ping -c 3 -t 5 $tunnel2
+	atf_check -s exit:0 -o ignore jexec wgtest2 ping -c 3 -t 5 $tunnel1
+}
+
+wg_basic_cleanup()
+{
+	vnet_cleanup
+}
+
+atf_init_test_cases()
+{
+	atf_add_test_case "wg_basic"
+}