Refactor neighbor_advertiser script and use mock for testing (sonic-net#1427)

Refactored code in neighbor_advertiser script and used mock module to unittesting

Author: sumukhatv

scripts/neighbor_advertiser

@@ -226,6 +226,23 @@ def get_vlan_addr_prefix(vlan_intf_name, ip_ver):
     return vlan_addr, vlan_prefix
 
 
+def get_link_local_addr(vlan_interface):
+    try:
+        out = subprocess.check_output(['ip', '-6', 'addr', 'show', vlan_interface])
+        out = out.decode('UTF-8')
+        for line in out.splitlines():
+            keys = line.split()
+            if keys[0] == 'inet6':
+                ip = IPNetwork(keys[1])
+                if str(ip.ip).startswith("fe80"):
+                    # Link local ipv6 address
+                    return str(ip.ip)
+    except Exception:
+        log.log_error('failed to get %s addresses from o.s.' % vlan_interface)
+    
+    return None
+
+
 def get_vlan_addresses(vlan_interface):
     vlan_id = get_vlan_interface_vlan_id(vlan_interface)
     vxlan_id = get_vlan_interface_vxlan_id(vlan_interface)
@@ -235,19 +252,10 @@ def get_vlan_addresses(vlan_interface):
     ipv6_addr, ipv6_prefix = get_vlan_addr_prefix(vlan_interface, 6)
 
     if len(ipv6_addr):
-        try:
-            out = subprocess.check_output(['ip', '-6', 'addr', 'show', vlan_interface])
-            out = out.decode('UTF-8')
-            for line in out.splitlines():
-                keys = line.split()
-                if keys[0] == 'inet6':
-                    ip = IPNetwork(keys[1])
-                    if str(ip.ip).startswith("fe80") and str(ip.ip) not in ipv6_addr:
-                        # Link local ipv6 address
-                        ipv6_addr.append(str(ip.ip))
-                        ipv6_prefix.append('128')
-        except Exception:
-            log.log_error('failed to get %s addresses from o.s.' % vlan_interface)
+        link_local_addr = get_link_local_addr(vlan_interface)
+        if link_local_addr and link_local_addr not in ipv6_addr:
+            ipv6_addr.append(link_local_addr)
+            ipv6_prefix.append('128')
 
     metadata = config_db.get_table('DEVICE_METADATA')
     mac_addr = metadata['localhost']['mac']

tests/neighbor_advertiser_test.py

@@ -1,6 +1,7 @@
 import sys
 import os
 import pytest
+from unittest import mock
 import subprocess
 from swsscommon.swsscommon import ConfigDBConnector
 
@@ -20,16 +21,7 @@ def set_up(self):
         neighbor_advertiser.connect_app_db()
 
     def test_neighbor_advertiser_slice(self, set_up):
-        cmd = "sudo sysctl -w net.ipv6.conf.all.disable_ipv6=0"
-        subprocess.check_output(cmd.split())
-        cmd = "sudo ip link add Vlan1000 type dummy"
-        subprocess.check_output(cmd.split())
-        cmd = "sudo ip -6 address add dev Vlan1000 scope link fe80::1e34:daff:fe1e:2800/64"
-        subprocess.check_output(cmd.split())
-        cmd = "sudo ip link add Vlan2000 type dummy"
-        subprocess.check_output(cmd.split())
-        cmd = "sudo ip -6 address add dev Vlan2000 scope link fe80::1e43:dfaf:fe2e:1800/64"
-        subprocess.check_output(cmd.split())
+        neighbor_advertiser.get_link_local_addr = mock.MagicMock(return_value='fe80::1e34:daff:fe1e:2800')
         output = neighbor_advertiser.construct_neighbor_advertiser_slice()
         expected_output = dict(
             {
@@ -53,7 +45,7 @@ def test_neighbor_advertiser_slice(self, set_up):
                         ],
                         'ipv6AddrMappings': [
                             {'macAddr': '1d:34:db:16:a6:00', 'ipAddr': 'fc02:1011::1', 'ipPrefixLen': '64'},
-                            {'macAddr': '1d:34:db:16:a6:00', 'ipAddr': 'fe80::1e43:dfaf:fe2e:1800', 'ipPrefixLen': '128'}
+                            {'macAddr': '1d:34:db:16:a6:00', 'ipAddr': 'fe80::1e34:daff:fe1e:2800', 'ipPrefixLen': '128'}
                         ],
                         'vxlanId': '2000',
                         'vlanId': '2000',