fix: adding more test case for table constraints property

Author: lkhagvadorj-amp

tests/unit/test_table.py

@@ -1000,6 +1000,19 @@ def test_table_constraints_property_setter_only_foriegn_keys(self):
             ]
         }
 
+    def test_table_constraints_property_setter_no_constraints(self):
+        from google.cloud.bigquery.table import TableConstraints
+
+        dataset = DatasetReference(self.PROJECT, self.DS_ID)
+        table_ref = dataset.table(self.TABLE_NAME)
+        table = self._make_one(table_ref)
+
+
+        table_constraints = TableConstraints(primary_key=None, foreign_keys=None)
+        table.table_constraints = table_constraints
+
+        assert table._properties["tableConstraints"] == {}    
+
     def test_description_setter_bad_value(self):
         dataset = DatasetReference(self.PROJECT, self.DS_ID)
         table_ref = dataset.table(self.TABLE_NAME)