tests: add tests for link executor

tests/Kyuafile

@@ -5,3 +5,5 @@ test_suite('ifupdown-ng')
 atf_test_program{name='ifquery_test'}
 atf_test_program{name='ifup_test'}
 atf_test_program{name='ifdown_test'}
+
+include('linux/Kyuafile')

tests/linux/Kyuafile

@@ -0,0 +1,5 @@
+syntax(2)
+
+test_suite('ifupdown-ng')
+
+atf_test_program{name='link_test'}

tests/linux/link_test

@@ -0,0 +1,18 @@
+#!/usr/bin/env atf-sh
+
+. $(atf_get_srcdir)/../test_env.sh
+EXECUTOR="$(atf_get_srcdir)/../../executor-scripts/linux/link"
+
+tests_init up down
+
+up_body() {
+	export IFACE=lo PHASE=up MOCK=echo
+	atf_check -s exit:0 -o match:'ip link set up dev lo' \
+		${EXECUTOR}
+}
+
+down_body() {
+	export IFACE=lo PHASE=down MOCK=echo
+	atf_check -s exit:0 -o match:'ip link set down dev lo' \
+		${EXECUTOR}
+}