improve unit test coverage for fast-reboot-dump script (sonic-net#4154)

What I did
enhances unit test coverage for scripts/fast-reboot-dump.py

generate_default_route_entries
generate_media_config
generate_fdb_entries
generate_neighbor_entries
This partially fixes sonic-net#1175 by increasing coverage of the fast-reboot-dump, coverage improving from 48.5% to 70%

How I did it
How to verify it
coverage after this unit test

scripts/fast-reboot-dump.py                              270     71     82     12    70%

Author: maipbui

tests/fast_reboot_dump_test.py

@@ -3,6 +3,9 @@
 from deepdiff import DeepDiff
 from utilities_common.db import Db
 import importlib
+import tempfile
+from unittest import mock
+from .mock_tables import dbconnector
 fast_reboot_dump = importlib.import_module("scripts.fast-reboot-dump")
 
 class TestFastRebootDump(object):
@@ -23,7 +26,7 @@ def setup_class(cls):
         cls.app_db = app_db
 
     #Test fast-reboot-dump script to generate all required objects when there is a VLAN interface with a PortChannel member.
-    def test_generate_fdb_entries_vlan_portcahnnel_member(self):
+    def test_generate_fdb_entries_vlan_portchannel_member(self):
         vlan_ifaces = ['Vlan2']
 
         fdb_entries, all_available_macs, map_mac_ip_per_vlan = fast_reboot_dump.generate_fdb_entries_logic(self.asic_db, self.app_db, vlan_ifaces)
@@ -36,7 +39,128 @@ def test_generate_fdb_entries_vlan_portcahnnel_member(self):
 
         expectd_map_mac_ip_per_vlan = {'Vlan2': {'52:54:00:5d:fc:b7': 'PortChannel0001'}}
         assert not DeepDiff(map_mac_ip_per_vlan, expectd_map_mac_ip_per_vlan, ignore_order=True)
-    
+
+    @mock.patch.object(fast_reboot_dump.syslog, "syslog", return_value=None)
+    @mock.patch.object(fast_reboot_dump, "SonicV2Connector")
+    def test_generate_neighbor_entries(self, mock_sonicv2, _mock_syslog):
+        conn = dbconnector.SonicV2Connector()
+        mock_sonicv2.return_value = conn
+
+        conn.connect(conn.APPL_DB)
+
+        # Included: (Vlan2, mac) is present in all_available_macs
+        key_included = 'NEIGH_TABLE:Vlan2:192.168.0.2'
+        conn.set(conn.APPL_DB, key_included, 'neigh', '52:54:00:5D:FC:B7')
+
+        # Excluded: exists in DB, but (Vlan3, mac) is NOT present in all_available_macs
+        # so generate_neighbor_entries() skip it
+        key_excluded = 'NEIGH_TABLE:Vlan3:192.168.0.3'
+        conn.set(conn.APPL_DB, key_excluded, 'neigh', 'aa:bb:cc:dd:ee:ff')
+
+        all_available_macs = {('Vlan2', '52:54:00:5d:fc:b7')}
+
+        with tempfile.TemporaryDirectory() as tmpdir:
+            outfile = os.path.join(tmpdir, 'arp.json')
+
+            neighbor_entries = fast_reboot_dump.generate_neighbor_entries(
+                outfile, all_available_macs
+            )
+
+            assert neighbor_entries == [
+                ('Vlan2', '52:54:00:5d:fc:b7', '192.168.0.2')
+            ]
+
+            with open(outfile) as fp:
+                data = json.load(fp)
+
+        assert len(data) == 1
+        obj = data[0]
+        assert key_included in obj
+        assert obj[key_included]['neigh'] == '52:54:00:5D:FC:B7'
+        assert obj['OP'] == 'SET'
+        assert not any(key_excluded in item for item in data)
+
+    @mock.patch.object(fast_reboot_dump, "SonicV2Connector")
+    def test_generate_default_route_entries(self, mock_sonicv2):
+        conn = dbconnector.SonicV2Connector()
+        mock_sonicv2.return_value = conn
+
+        conn.connect(conn.APPL_DB)
+        conn.set(conn.APPL_DB, 'ROUTE_TABLE:0.0.0.0/0', 'nexthop', '10.0.0.1')
+        conn.set(conn.APPL_DB, 'ROUTE_TABLE:0.0.0.0/0', 'ifname', 'Ethernet0')
+        conn.set(conn.APPL_DB, 'ROUTE_TABLE::/0', 'nexthop', '2001:db8::1')
+        conn.set(conn.APPL_DB, 'ROUTE_TABLE::/0', 'ifname', 'Ethernet0')
+
+        with tempfile.TemporaryDirectory() as tmpdir:
+            outfile = os.path.join(tmpdir, 'default_routes.json')
+            fast_reboot_dump.generate_default_route_entries(outfile)
+
+            with open(outfile) as fp:
+                data = json.load(fp)
+
+        ipv4_obj = next(item for item in data if 'ROUTE_TABLE:0.0.0.0/0' in item)
+        assert ipv4_obj['ROUTE_TABLE:0.0.0.0/0']['nexthop'] == '10.0.0.1'
+        assert ipv4_obj['ROUTE_TABLE:0.0.0.0/0']['ifname'] == 'Ethernet0'
+        assert ipv4_obj['OP'] == 'SET'
+
+        ipv6_candidates = [item for item in data if 'ROUTE_TABLE::/0' in item]
+        if ipv6_candidates:
+            ipv6_obj = ipv6_candidates[0]
+            assert ipv6_obj['ROUTE_TABLE::/0']['nexthop'] == '2001:db8::1'
+            assert ipv6_obj['ROUTE_TABLE::/0']['ifname'] == 'Ethernet0'
+
+    @mock.patch.object(fast_reboot_dump, "SonicV2Connector")
+    def test_generate_media_config(self, mock_sonicv2):
+        conn = dbconnector.SonicV2Connector()
+        mock_sonicv2.return_value = conn
+
+        conn.connect(conn.APPL_DB)
+
+        key = 'PORT_TABLE:Ethernet0'
+        conn.set(conn.APPL_DB, key, 'preemphasis', '1')
+        conn.set(conn.APPL_DB, key, 'idriver', '2')
+        conn.set(conn.APPL_DB, key, 'speed', '100000')
+
+        with tempfile.TemporaryDirectory() as tmpdir:
+            outfile = os.path.join(tmpdir, 'media_config.json')
+            media_config = fast_reboot_dump.generate_media_config(outfile)
+
+            with open(outfile) as fp:
+                file_data = json.load(fp)
+
+        entry = next(item for item in media_config if key in item)
+        attrs = entry[key]
+        assert attrs == {
+            'preemphasis': '1',
+            'idriver': '2'
+        }
+        assert 'speed' not in attrs
+
+        file_entry = next(item for item in file_data if key in item)
+        assert file_entry[key] == attrs
+        assert entry['OP'] == 'SET'
+        assert file_entry['OP'] == 'SET'
+
+    @mock.patch.object(fast_reboot_dump, "get_vlan_ifaces", return_value=[])
+    @mock.patch.object(fast_reboot_dump, "SonicV2Connector")
+    def test_generate_fdb_entries(self, mock_sonicv2, _mock_get_vlan_ifaces):
+        conn = dbconnector.SonicV2Connector()
+        mock_sonicv2.return_value = conn
+
+        with tempfile.TemporaryDirectory() as tmpdir:
+            outfile = os.path.join(tmpdir, 'fdb.json')
+
+            all_available_macs, map_mac_ip_per_vlan = fast_reboot_dump.generate_fdb_entries(outfile)
+
+            assert all_available_macs == set()
+            assert map_mac_ip_per_vlan == {}
+
+            with open(outfile) as fp:
+                data = json.load(fp)
+
+            assert data == []
+
+
     @classmethod
     def teardown_class(cls):
         print("TEARDOWN")