yes: Add tests

MFC after:	1 week
Sponsored by:	Klara, Inc.
Reviewed by:	kevans
Differential Revision:	https://reviews.freebsd.org/D55802

etc/mtree/BSD.tests.dist

@@ -1265,6 +1265,8 @@
             yacc
             ..
         ..
+        yes
+        ..
     ..
     usr.sbin
         certctl

usr.bin/yes/Makefile

@@ -1,3 +1,7 @@
+.include <src.opts.mk>
+
 PROG=	yes
+HAS_TESTS=
+SUBDIR.${MK_TESTS}=	tests
 
 .include <bsd.prog.mk>

usr.bin/yes/tests/Makefile

@@ -0,0 +1,4 @@
+PACKAGE=	tests
+ATF_TESTS_SH=	yes_test
+
+.include <bsd.test.mk>

usr.bin/yes/tests/yes_test.sh

@@ -0,0 +1,85 @@
+#
+# Copyright (c) 2026 Klara, Inc.
+#
+# SPDX-License-Identifier: BSD-2-Clause
+#
+
+atf_test_case none
+none_head()
+{
+	atf_set "descr" "No arguments"
+}
+none_body()
+{
+	atf_check \
+	    -o inline:"y\ny\ny\ny\ny\n" \
+	    -x "yes | head -5"
+}
+
+atf_test_case one
+one_head()
+{
+	atf_set "descr" "One argument"
+}
+one_body()
+{
+	local y="Hello, world!"
+	atf_check \
+	    -o inline:"${y}\n${y}\n${y}\n${y}\n${y}\n" \
+	    -x "yes '${y}' | head -5"
+}
+
+atf_test_case multi
+multi_head()
+{
+	atf_set "descr" "Multiple arguments"
+}
+multi_body()
+{
+	set -- The Magic Words are Squeamish Ossifrage
+	local y="$*"
+	atf_check \
+	    -o inline:"${y}\n${y}\n${y}\n${y}\n${y}\n" \
+	    -x "yes $* | head -5"
+}
+
+atf_test_case argv
+argv_head()
+{
+	atf_set "descr" "Verify that argv is unmolested"
+}
+argv_body()
+{
+	yes y >/dev/null &
+	local pid=$!
+	atf_check -o inline:"yes y\n" ps -o args= $pid
+	kill $pid
+	wait
+}
+
+atf_test_case stdout
+stdout_head()
+{
+	atf_set descr "Error writing to stdout"
+}
+stdout_body()
+{
+	(
+		trap "" PIPE
+		# Give true(1) some time to exit.
+		sleep 1
+		yes 2>stderr
+		echo $? >result
+	) | true
+	atf_check -o inline:"1\n" cat result
+	atf_check -o match:"stdout" cat stderr
+}
+
+atf_init_test_cases()
+{
+	atf_add_test_case none
+	atf_add_test_case one
+	atf_add_test_case multi
+	atf_add_test_case argv
+	atf_add_test_case stdout
+}