tests: add tests for deferred interface teardown (refcounting)

tests/fixtures/deferred-teardown-1.ifstate

@@ -0,0 +1,6 @@
+lo=lo 1
+br0=br0 1
+bond0=bond0 2
+eth0=eth0 3
+eth1=eth1 2
+tun0=tun0 1

tests/fixtures/deferred-teardown-1.interfaces

@@ -0,0 +1,9 @@
+auto br0
+iface br0
+	requires bond0
+
+iface bond0
+	requires eth0 eth1
+
+iface tun0
+	requires eth0

tests/fixtures/deferred-teardown-2.ifstate

@@ -0,0 +1,5 @@
+eth0=eth0 5
+tun0=tun0 1
+tun1=tun1 1
+tun2=tun2 1
+tun3=tun3 1

tests/fixtures/deferred-teardown-2.interfaces

@@ -0,0 +1,11 @@
+iface tun0
+	requires eth0
+
+iface tun1
+	requires eth0
+
+iface tun2
+	requires eth0
+
+iface tun3
+	requires eth0

tests/ifdown_test

@@ -19,6 +19,9 @@ tests_init \
 	learned_dependency_2 \
 	learned_executor \
 	implicit_vlan \
+	deferred_teardown_1 \
+	deferred_teardown_2 \
+	deferred_teardown_3 \
 	regress_opt_f
 
 noargs_body() {
@@ -142,6 +145,33 @@ implicit_vlan_body() {
 		ifdown -n -S $FIXTURES/vlan.ifstate -E $EXECUTORS -i $FIXTURES/vlan.interfaces eth0.8
 }
 
+deferred_teardown_1_body() {
+	atf_check -s exit:0 -o ignore \
+		-e match:"skipping dependent interface eth0 \\(of bond0\\) -- transient dependencies still exist" \
+		-e match:"changing state of dependent interface eth1 \\(of bond0\\) to down" \
+		ifdown -n -S $FIXTURES/deferred-teardown-1.ifstate -E $EXECUTORS \
+			-i $FIXTURES/deferred-teardown-1.interfaces br0
+}
+
+deferred_teardown_2_body() {
+	atf_check -s exit:0 -o ignore \
+		-e match:"skipping dependent interface eth0 \\(of tun0\\) -- transient dependencies still exist" \
+		-e match:"skipping dependent interface eth0 \\(of tun1\\) -- transient dependencies still exist" \
+		-e match:"skipping dependent interface eth0 \\(of tun2\\) -- transient dependencies still exist" \
+		ifdown -n -S $FIXTURES/deferred-teardown-2.ifstate -E $EXECUTORS \
+			-i $FIXTURES/deferred-teardown-2.interfaces tun0 tun1 tun2
+}
+
+deferred_teardown_3_body() {
+	atf_check -s exit:0 -o ignore \
+		-e match:"skipping dependent interface eth0 \\(of tun0\\) -- transient dependencies still exist" \
+		-e match:"skipping dependent interface eth0 \\(of tun1\\) -- transient dependencies still exist" \
+		-e match:"skipping dependent interface eth0 \\(of tun2\\) -- transient dependencies still exist" \
+		-e match:"changing state of dependent interface eth0 \\(of tun3\\) to down" \
+		ifdown -n -S $FIXTURES/deferred-teardown-2.ifstate -E $EXECUTORS \
+			-i $FIXTURES/deferred-teardown-2.interfaces tun0 tun1 tun2 tun3
+}
+
 regress_opt_f_body() {
 	atf_check -s exit:0 -o ignore -e ignore \
 		ifdown -n -S $FIXTURES/vlan.ifstate -E $EXECUTORS -i $FIXTURES/vlan.interfaces -f eth0.8