[vlan] Add pytest case to add max vlan. (sonic-net#881)

* [vlan] Add pytest case to add max vlan.

Signed-off-by: Emma Lin <emma_lin@edge-core.com>

tests/test_vlan.py

@@ -251,3 +251,30 @@ def test_AddVlanWithIncorrectValueType(self, dvs, testlog, test_input, expected)
             #remove vlan
             self.remove_vlan(vlan)
 
+    def test_AddMaxVlan(self, dvs, testlog):
+        self.setup_db(dvs)
+
+        min_vid = 2
+        max_vid = 4094
+
+        # create max vlan
+        vlan = min_vid
+        while vlan <= max_vid:
+            self.create_vlan(str(vlan))
+            vlan += 1
+
+        # check asic database
+        tbl = swsscommon.Table(self.adb, "ASIC_STATE:SAI_OBJECT_TYPE_VLAN")
+        vlan_entries = [k for k in tbl.getKeys() if k != dvs.asicdb.default_vlan_id]
+        assert len(vlan_entries) == (4094-1)
+
+        # remove all vlan
+        vlan = min_vid
+        while vlan <= max_vid:
+            self.remove_vlan(str(vlan))
+            vlan += 1
+
+        # check asic database
+        tbl = swsscommon.Table(self.adb, "ASIC_STATE:SAI_OBJECT_TYPE_VLAN")
+        vlan_entries = [k for k in tbl.getKeys() if k != dvs.asicdb.default_vlan_id]
+        assert len(vlan_entries) == 0