Add override testcase to verify removal (#2288)

What I did
Add one override-config-table testcase to verify empty table removal.

How I did it
Add the testcase to verify the removal.

How to verify it
Unit test.

Author: wen587

tests/config_override_input/empty_table_removal.json

@@ -0,0 +1,96 @@
+{
+    "running_config": {
+        "ACL_TABLE": {
+            "DATAACL": {
+                "policy_desc": "DATAACL",
+                "ports": [
+                    "Ethernet4"
+                ],
+                "stage": "ingress",
+                "type": "L3"
+            },
+            "NTP_ACL": {
+                "policy_desc": "NTP_ACL",
+                "services": [
+                    "NTP"
+                ],
+                "stage": "ingress",
+                "type": "CTRLPLANE"
+            }
+        },
+        "AUTO_TECHSUPPORT_FEATURE": {
+            "bgp": {
+                "rate_limit_interval": "600",
+                "state": "enabled"
+            },
+            "database": {
+                "rate_limit_interval": "600",
+                "state": "enabled"
+            }
+        },
+        "PORT": {
+            "Ethernet4": {
+                "admin_status": "up",
+                "alias": "fortyGigE0/4",
+                "description": "Servers0:eth0",
+                "index": "1",
+                "lanes": "29,30,31,32",
+                "mtu": "9100",
+                "pfc_asym": "off",
+                "speed": "40000",
+                "tpid": "0x8100"
+            },
+            "Ethernet8": {
+                "admin_status": "up",
+                "alias": "fortyGigE0/8",
+                "description": "Servers1:eth0",
+                "index": "2",
+                "lanes": "33,34,35,36",
+                "mtu": "9100",
+                "pfc_asym": "off",
+                "speed": "40000",
+                "tpid": "0x8100"
+            }
+        }
+    },
+    "golden_config": {
+        "ACL_TABLE": {
+        }
+    },
+    "expected_config": {
+        "AUTO_TECHSUPPORT_FEATURE": {
+            "bgp": {
+                "rate_limit_interval": "600",
+                "state": "enabled"
+            },
+            "database": {
+                "rate_limit_interval": "600",
+                "state": "enabled"
+            }
+        },
+        "PORT": {
+            "Ethernet4": {
+                "admin_status": "up",
+                "alias": "fortyGigE0/4",
+                "description": "Servers0:eth0",
+                "index": "1",
+                "lanes": "29,30,31,32",
+                "mtu": "9100",
+                "pfc_asym": "off",
+                "speed": "40000",
+                "tpid": "0x8100"
+            },
+            "Ethernet8": {
+                "admin_status": "up",
+                "alias": "fortyGigE0/8",
+                "description": "Servers1:eth0",
+                "index": "2",
+                "lanes": "33,34,35,36",
+                "mtu": "9100",
+                "pfc_asym": "off",
+                "speed": "40000",
+                "tpid": "0x8100"
+            }
+        }
+    }
+}

tests/config_override_test.py

@@ -16,6 +16,7 @@
 NEW_FEATURE_CONFIG = os.path.join(DATA_DIR, "new_feature_config.json")
 FULL_CONFIG_OVERRIDE = os.path.join(DATA_DIR, "full_config_override.json")
 PORT_CONFIG_OVERRIDE = os.path.join(DATA_DIR, "port_config_override.json")
+EMPTY_TABLE_REMOVAL = os.path.join(DATA_DIR, "empty_table_removal.json")
 
 # Load sonic-cfggen from source since /usr/local/bin/sonic-cfggen does not have .py extension.
 sonic_cfggen = load_module_from_source('sonic_cfggen', '/usr/local/bin/sonic-cfggen')
@@ -137,6 +138,15 @@ def test_golden_config_db_port_config(self):
             db, config, read_data['running_config'], read_data['golden_config'],
             read_data['expected_config'])
 
+    def test_golden_config_db_empty_table_removal(self):
+        """Golden Config empty table does table removal"""
+        db = Db()
+        with open(EMPTY_TABLE_REMOVAL, "r") as f:
+            read_data = json.load(f)
+        self.check_override_config_table(
+            db, config, read_data['running_config'], read_data['golden_config'],
+            read_data['expected_config'])
+
     def check_override_config_table(self, db, config, running_config,
                                     golden_config, expected_config):
         def read_json_file_side_effect(filename):