Add test for subnet gateway IPv4 and IPv6

Four tests were added for testing neutron subnets with and
without gateway defined as a subnet attribute (gateway_ip)

Change-Id: I7862da41e62a47c274f170d29ceeeaeb89b2c976
Implements: blueprint neutron-subnet-attributes
diff --git a/tempest/api/network/base.py b/tempest/api/network/base.py
index 696a1c3..5d7e07a 100644
--- a/tempest/api/network/base.py
+++ b/tempest/api/network/base.py
@@ -145,7 +145,7 @@
         return network
 
     @classmethod
-    def create_subnet(cls, network):
+    def create_subnet(cls, network, gateway=None):
         """Wrapper utility that returns a test subnet."""
         # The cidr and mask_bits depend on the ip version.
         if cls._ip_version == 4:
@@ -156,14 +156,19 @@
             mask_bits = CONF.network.tenant_network_v6_mask_bits
         # Find a cidr that is not in use yet and create a subnet with it
         for subnet_cidr in cidr.subnet(mask_bits):
+            if not gateway:
+                gateway = str(netaddr.IPAddress(subnet_cidr) + 1)
             try:
                 resp, body = cls.client.create_subnet(
                     network_id=network['id'],
                     cidr=str(subnet_cidr),
-                    ip_version=cls._ip_version)
+                    ip_version=cls._ip_version,
+                    gateway_ip=gateway)
                 break
             except exceptions.BadRequest as e:
                 is_overlapping_cidr = 'overlaps with another subnet' in str(e)
+                # Unset gateway value if there is an overlapping subnet
+                gateway = None
                 if not is_overlapping_cidr:
                     raise
         else:
diff --git a/tempest/api/network/test_networks.py b/tempest/api/network/test_networks.py
index de44f4d..452bd61 100644
--- a/tempest/api/network/test_networks.py
+++ b/tempest/api/network/test_networks.py
@@ -216,6 +216,37 @@
         # it from the list.
         self.subnets.pop()
 
+    @test.attr(type='smoke')
+    def test_create_delete_subnet_with_gw(self):
+        gateway = '10.100.0.13'
+        name = data_utils.rand_name('network-')
+        resp, body = self.client.create_network(name=name)
+        self.assertEqual('201', resp['status'])
+        network = body['network']
+        net_id = network['id']
+        subnet = self.create_subnet(network, gateway)
+        # Verifies Subnet GW in IPv4
+        self.assertEqual(subnet['gateway_ip'], gateway)
+        # Delete network and subnet
+        resp, body = self.client.delete_network(net_id)
+        self.assertEqual('204', resp['status'])
+        self.subnets.pop()
+
+    @test.attr(type='smoke')
+    def test_create_delete_subnet_without_gw(self):
+        name = data_utils.rand_name('network-')
+        resp, body = self.client.create_network(name=name)
+        self.assertEqual('201', resp['status'])
+        network = body['network']
+        net_id = network['id']
+        subnet = self.create_subnet(network)
+        # Verifies Subnet GW in IPv4
+        self.assertEqual(subnet['gateway_ip'], '10.100.0.1')
+        # Delete network and subnet
+        resp, body = self.client.delete_network(net_id)
+        self.assertEqual('204', resp['status'])
+        self.subnets.pop()
+
 
 class NetworksTestXML(NetworksTestJSON):
     _interface = 'xml'
@@ -370,6 +401,37 @@
             skip_msg = "IPv6 Tests are disabled."
             raise cls.skipException(skip_msg)
 
+    @test.attr(type='smoke')
+    def test_create_delete_subnet_with_gw(self):
+        gateway = '2003::2'
+        name = data_utils.rand_name('network-')
+        resp, body = self.client.create_network(name=name)
+        self.assertEqual('201', resp['status'])
+        network = body['network']
+        net_id = network['id']
+        subnet = self.create_subnet(network, gateway)
+        # Verifies Subnet GW in IPv6
+        self.assertEqual(subnet['gateway_ip'], gateway)
+        # Delete network and subnet
+        resp, body = self.client.delete_network(net_id)
+        self.assertEqual('204', resp['status'])
+        self.subnets.pop()
+
+    @test.attr(type='smoke')
+    def test_create_delete_subnet_without_gw(self):
+        name = data_utils.rand_name('network-')
+        resp, body = self.client.create_network(name=name)
+        self.assertEqual('201', resp['status'])
+        network = body['network']
+        net_id = network['id']
+        subnet = self.create_subnet(network)
+        # Verifies Subnet GW in IPv6
+        self.assertEqual(subnet['gateway_ip'], '2003::1')
+        # Delete network and subnet
+        resp, body = self.client.delete_network(net_id)
+        self.assertEqual('204', resp['status'])
+        self.subnets.pop()
+
 
 class NetworksIpV6TestXML(NetworksIpV6TestJSON):
     _interface = 'xml'