Write up some basic tests for readlink(1)

The tests exercise -f (f_flag), -n (n_flag), and no arguments (basic).

MFC after:	1 month
Sponsored by:	Dell EMC Isilon

etc/mtree/BSD.tests.dist

@@ -670,6 +670,8 @@
         ..
         soelim
         ..
+        stat
+        ..
         tail
         ..
         tar

usr.bin/stat/Makefile

@@ -1,8 +1,12 @@
 # $FreeBSD$
 
+.include <src.opts.mk>
+
 PROG=	stat
 
 LINKS=	${BINDIR}/stat ${BINDIR}/readlink
 MLINKS=	stat.1 readlink.1
 
+SUBDIR.${MK_TESTS}+=	tests
+
 .include <bsd.prog.mk>

usr.bin/stat/stat.1

@@ -29,7 +29,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd April 22, 2012
+.Dd June 22, 2017
 .Dt STAT 1
 .Os
 .Sh NAME

usr.bin/stat/tests/Makefile

@@ -0,0 +1,5 @@
+# $FreeBSD$
+
+ATF_TESTS_SH+=	readlink_test
+
+.include <bsd.test.mk>

usr.bin/stat/tests/readlink_test.sh

@@ -0,0 +1,73 @@
+#
+# Copyright (c) 2017 Dell EMC
+# 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.
+#
+# $FreeBSD$
+
+atf_test_case f_flag
+basic_head()
+{
+	atf_set	"descr" "Verify that calling readlink without any flags " \
+			"prints out the symlink target for a file"
+}
+basic_body()
+{
+	atf_check ln -s foo bar
+	atf_check -o inline:'foo\n' readlink bar
+}
+
+atf_test_case f_flag
+f_flag_head()
+{
+	atf_set	"descr" "Verify that calling readlink with -f will not emit " \
+			"an error message/exit with a non-zero code"
+}
+f_flag_body()
+{
+	atf_check touch A.file
+	atf_check ln -s nonexistent A.link
+	atf_check -o inline:"nonexistent\n" \
+	    -s exit:1 readlink A.file A.link
+	atf_check -o inline:"$(realpath A.file)\n$PWD/nonexistent\n" \
+	    -s exit:1 readlink -f A.file A.link
+}
+
+atf_test_case n_flag
+n_flag_head()
+{
+}
+n_flag_body()
+{
+	atf_check ln -s nonexistent.A A
+	atf_check ln -s nonexistent.B B
+	atf_check -o 'inline:nonexistent.A\nnonexistent.B\n' readlink A B
+	atf_check -o 'inline:nonexistent.Anonexistent.B' readlink -n A B
+}
+
+atf_init_test_cases()
+{
+	atf_add_test_case basic
+	atf_add_test_case f_flag
+	atf_add_test_case n_flag
+}