smoketest: loopback: interface can not be deleted, it must always exist

Commit 35b049aa ("smoketest: interfaces: verify deletion of interfaces")
validated that when the test completed (tearDown()) there must be no
interfaces left registered for the tests. This is invalid for the loopback
interface as it can not be deleted from the system.

(cherry picked from commit b373d3841608838fd28f98691cb14e42c128c216)

2 files changed, 14 insertions, 2 deletions

diff --git a/smoketest/scripts/cli/base_interfaces_test.py b/smoketest/scripts/cli/base_interfaces_test.py
index fbedca3f3..8b25d85e6 100644
--- a/smoketest/scripts/cli/base_interfaces_test.py
+++ b/smoketest/scripts/cli/base_interfaces_test.py
@@ -18,9 +18,10 @@ import json
 
 from binascii import hexlify
 
-from netifaces import ifaddresses
 from netifaces import AF_INET
 from netifaces import AF_INET6
+from netifaces import ifaddresses
+from netifaces import interfaces
 
 from vyos.configsession import ConfigSession
 from vyos.ifconfig import Interface
@@ -96,7 +97,7 @@ class BasicInterfaceTest:
             # Ethernet is handled in its derived class
             if 'ethernet' not in self._base_path:
                 for intf in self._interfaces:
-                    self.assertFalse(os.path.isdir('/sys/class/net/{intf}'))
+                    self.assertTrue(intf not in interfaces())
 
         def test_span_mirror(self):
             if not self._mirror_interfaces:
diff --git a/smoketest/scripts/cli/test_interfaces_loopback.py b/smoketest/scripts/cli/test_interfaces_loopback.py
index 79225a1bd..e3538fc59 100755
--- a/smoketest/scripts/cli/test_interfaces_loopback.py
+++ b/smoketest/scripts/cli/test_interfaces_loopback.py
@@ -17,6 +17,8 @@
 import unittest
 
 from base_interfaces_test import BasicInterfaceTest
+from netifaces import interfaces
+
 from vyos.validate import is_intf_addr_assigned
 
 class LoopbackInterfaceTest(BasicInterfaceTest.BaseTest):
@@ -27,6 +29,15 @@ class LoopbackInterfaceTest(BasicInterfaceTest.BaseTest):
          self._base_path = ['interfaces', 'loopback']
          self._interfaces = ['lo']
 
+    def tearDown(self):
+        self.session.delete(self._base_path)
+        self.session.commit()
+        del self.session
+
+        # loopback interface must persist!
+        for intf in self._interfaces:
+            self.assertTrue(intf in interfaces())
+
     def test_add_single_ip_address(self):
         super().test_add_single_ip_address()
         for addr in self._loopback_addresses: