tsort: Add unit tests.

MFC after:	1 week
Sponsored by:	Klara, Inc.
Reviewed by:	markj
Differential Revision:	https://reviews.freebsd.org/D40043

etc/mtree/BSD.tests.dist

@@ -1116,6 +1116,8 @@
         ..
         truncate
         ..
+        tsort
+        ..
         units
         ..
         unifdef

usr.bin/tsort/Makefile

@@ -1,6 +1,11 @@
 #	@(#)Makefile	8.1 (Berkeley) 6/9/93
 # $FreeBSD$
 
+.include <src.opts.mk>
+
 PROG=	tsort
 
+HAS_TESTS=
+SUBDIR.${MK_TESTS}=	tests
+
 .include <bsd.prog.mk>

usr.bin/tsort/tests/Makefile

@@ -0,0 +1,6 @@
+PACKAGE=	tests
+
+ATF_TESTS_SH=	tsort_test
+BINDIR=		${TESTSDIR}
+
+.include <bsd.test.mk>

usr.bin/tsort/tests/tsort_test.sh

@@ -0,0 +1,66 @@
+#
+# Copyright (c) 2023 Klara, Inc.
+#
+# SPDX-License-Identifier: BSD-2-Clause
+#
+
+atf_test_case basic
+basic_head()
+{
+	atf_set "descr" "Sort a basic graph"
+}
+basic_body()
+{
+	cat >input <<EOF
+A B
+A F
+B C
+B D
+D E
+EOF
+	cat >output <<EOF
+A
+F
+B
+D
+C
+E
+EOF
+	atf_check -o file:output tsort input
+	atf_check -o file:output tsort <input
+}
+
+atf_test_case cycle
+cycle_head()
+{
+	atf_set "descr" "Sort a graph with a cycle"
+}
+cycle_body()
+{
+	cat >input <<EOF
+A B
+A F
+B C
+B D
+D E
+D A
+EOF
+	cat >output<<EOF
+D
+E
+A
+F
+B
+C
+EOF
+	atf_check -e match:cycle -o file:output tsort input
+	atf_check -e match:cycle -o file:output tsort <input
+	atf_check -o file:output tsort -q input
+	atf_check -o file:output tsort -q <input
+}
+
+atf_init_test_cases()
+{
+	atf_add_test_case basic
+	atf_add_test_case cycle
+}