diff --git a/etc/mtree/BSD.tests.dist b/etc/mtree/BSD.tests.dist
index 19b0ccc25936..394b2ec90dcd 100644
--- a/etc/mtree/BSD.tests.dist
+++ b/etc/mtree/BSD.tests.dist
@@ -1070,6 +1070,8 @@
         ..
         procstat
         ..
+        renice
+        ..
         rs
         ..
         sdiff
diff --git a/usr.bin/renice/Makefile b/usr.bin/renice/Makefile
index d5471379fe1e..8baf6936d7bc 100644
--- a/usr.bin/renice/Makefile
+++ b/usr.bin/renice/Makefile
@@ -1,7 +1,12 @@
 #	@(#)Makefile	8.1 (Berkeley) 6/9/93
 # $FreeBSD$
 
+.include <src.opts.mk>
+
 PROG=	renice
 MAN=	renice.8
 
+HAS_TESTS=
+SUBDIR.${MK_TESTS}+= tests
+
 .include <bsd.prog.mk>
diff --git a/usr.bin/renice/tests/Makefile b/usr.bin/renice/tests/Makefile
new file mode 100644
index 000000000000..c252e396811c
--- /dev/null
+++ b/usr.bin/renice/tests/Makefile
@@ -0,0 +1,3 @@
+ATF_TESTS_SH+=	renice_test
+
+.include <bsd.test.mk>
diff --git a/usr.bin/renice/tests/renice_test.sh b/usr.bin/renice/tests/renice_test.sh
new file mode 100644
index 000000000000..323fe44591c8
--- /dev/null
+++ b/usr.bin/renice/tests/renice_test.sh
@@ -0,0 +1,169 @@
+#!/bin/sh
+#-
+# Copyright (c) 2022 Klara, Inc.
+# 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.
+#
+
+# Name of user to use for -u tests when running as root.  Beware that
+# processes owned by that user will be affected by the test.
+TEST_USER=nobody
+
+_renice() {
+	atf_check -o empty -e ignore -s exit:0 renice "$@"
+}
+
+# Set a process's nice number to an absolute value
+atf_test_case renice_abs_pid
+renice_abs_pid_body() {
+	local pid nice incr
+	sleep 60 &
+	pid=$!
+	nice="$(ps -o nice= -p $pid)"
+	incr=3
+	_renice $((nice+incr)) $pid
+	atf_check_equal $((nice+incr)) "$(ps -o nice= -p $pid)"
+	kill $pid
+}
+
+# Change a process's nice number by a relative value
+atf_test_case renice_rel_pid
+renice_rel_pid_body() {
+	local pid nice incr
+	sleep 60 &
+	pid=$!
+	nice="$(ps -o nice= -p $pid)"
+	incr=3
+	_renice -n $incr $pid
+	_renice -p -n $incr $pid
+	_renice -n $incr -p $pid
+	atf_check_equal $((nice+incr+incr+incr)) "$(ps -o nice= -p $pid)"
+	kill $pid
+}
+
+# Set a process group's nice number to an absolute value
+atf_test_case renice_abs_pgid
+renice_abs_pgid_body() {
+	local pid pgid nice incr
+	# make sure target runs in a different pgrp than ours
+	pid=$(sh -mc "sleep 60 >/dev/null & echo \$!")
+	pgid="$(ps -o pgid= -p $pid)"
+	nice="$(ps -o nice= -p $pid)"
+	incr=3
+	_renice $((nice+incr)) -g $pgid
+	atf_check_equal $((nice+incr)) "$(ps -o nice= -p $pid)"
+	kill $pid
+}
+
+# Change a process group's nice number by a relative value
+atf_test_case renice_rel_pgid
+renice_rel_pgid_body() {
+	local pid pgid nice incr
+	# make sure target runs in a different pgrp than ours
+	pid=$(sh -mc "sleep 60 >/dev/null & echo \$!")
+	pgid="$(ps -o pgid= -p $pid)"
+	nice="$(ps -o nice= -p $pid)"
+	incr=3
+	_renice -g -n $incr $pgid
+	_renice -n $incr -g $pgid
+	atf_check_equal $((nice+incr+incr)) "$(ps -o nice= -p $pid)"
+	kill $pid
+}
+
+# Set a user's processes' nice numbers to an absolute value
+atf_test_case renice_abs_user
+renice_abs_user_head() {
+	atf_set "require.user" "root"
+}
+renice_abs_user_body() {
+	local user pid nice incr
+	pid=$(su -m $TEST_USER -c "sleep 60 >/dev/null & echo \$!")
+	nice="$(ps -o nice= -p $pid)"
+	incr=3
+	_renice $((nice+incr)) -u $TEST_USER
+	atf_check_equal $((nice+incr)) "$(ps -o nice= -p $pid)"
+	kill $pid
+}
+
+# Change a user's processes' nice numbers by a relative value
+atf_test_case renice_rel_user
+renice_rel_user_head() {
+	atf_set "require.user" "root"
+}
+renice_rel_user_body() {
+	local user pid nice incr
+	pid=$(su -m $TEST_USER -c "sleep 60 >/dev/null & echo \$!")
+	nice="$(ps -o nice= -p $pid)"
+	incr=3
+	_renice -u -n $incr $TEST_USER
+	_renice -n $incr -u $TEST_USER
+	atf_check_equal $((nice+incr+incr)) "$(ps -o nice= -p $pid)"
+	kill $pid
+}
+
+# Test various delimiter positions
+atf_test_case renice_delim
+renice_delim_body() {
+	local pid nice incr
+	sleep 60 &
+	pid=$!
+	nice="$(ps -o nice= -p $pid)"
+	incr=0
+	# without -p
+	: $((incr=incr+1))
+	_renice -- $((nice+incr)) $pid
+	atf_check_equal $((nice+incr)) "$(ps -o nice= -p $pid)"
+	: $((incr=incr+1))
+	_renice $((nice+incr)) -- $pid
+	atf_check_equal $((nice+incr)) "$(ps -o nice= -p $pid)"
+	: $((incr=incr+1))
+	_renice $((nice+incr)) $pid --
+	atf_check_equal $((nice+incr)) "$(ps -o nice= -p $pid)"
+	# with -p
+	: $((incr=incr+1))
+	_renice -p -- $((nice+incr)) $pid
+	atf_check_equal $((nice+incr)) "$(ps -o nice= -p $pid)"
+	: $((incr=incr+1))
+	_renice -p $((nice+incr)) -- $pid
+	atf_check_equal $((nice+incr)) "$(ps -o nice= -p $pid)"
+	: $((incr=incr+1))
+	_renice -p $((nice+incr)) $pid --
+	atf_check_equal $((nice+incr)) "$(ps -o nice= -p $pid)"
+	: $((incr=incr+1))
+	_renice $((nice+incr)) -p -- $pid
+	atf_check_equal $((nice+incr)) "$(ps -o nice= -p $pid)"
+	: $((incr=incr+1))
+	_renice $((nice+incr)) -p $pid --
+	atf_check_equal $((nice+incr)) "$(ps -o nice= -p $pid)"
+	kill $pid
+}
+
+atf_init_test_cases() {
+	atf_add_test_case renice_abs_pid
+	atf_add_test_case renice_rel_pid
+	atf_add_test_case renice_abs_pgid
+	atf_add_test_case renice_rel_pgid
+	atf_add_test_case renice_abs_user
+	atf_add_test_case renice_rel_user
+	atf_add_test_case renice_delim
+}