test: Add test case for know failure on switching from DHCP to static

When switching from DHCP without DHCP server to static IPV6(IPv4
disabled), the nmstate will fail with verification failure showing IPv6
is still disabled.

The keys to reproduce the problem:
    * Dummy cannot work. Need to be veth.
    * Need to be newly created profile with DHCPv6 enable.
      Modifying existing profile to enable DHCPv6 cannot trigger this
      problem.

Add test case to track this problem in CI.

Signed-off-by: Gris Ge <fge@redhat.com>

tests/integration/dynamic_ip_test.py

@@ -34,6 +34,7 @@ from libnmstate.schema import InterfaceState
 from libnmstate.schema import Route as RT
 
 from libnmstate.error import NmstateNotImplementedError
+from libnmstate.error import NmstateVerificationError
 
 from .testlib import assertlib
 from .testlib import cmdlib
@@ -45,6 +46,8 @@ from .testlib.bridgelib import add_port_to_bridge
 from .testlib.bridgelib import create_bridge_subtree_state
 from .testlib.bridgelib import linux_bridge
 
+ETH1 = "eth1"
+
 DEFAULT_TIMEOUT = 20
 NM_DHCP_TIMEOUT_DEFAULT = 45
 # The default IPv6 RA/Autoconf timeout is 30 seconds, less than above.
@@ -1077,3 +1080,58 @@ def test_static_ip_with_routes_switch_back_to_dynamic(
         if route[RT.NEXT_HOP_INTERFACE] == DHCP_CLI_NIC
     ]
     assert not current_config_routes
+
+
+@pytest.fixture(scope="function")
+def eth1_with_dhcp6_no_dhcp_server():
+    # Cannot depend on eth1_up fixture as the reproducer requires the
+    # veth profile been created with DHCPv6 enabled.
+    iface_state = {
+        Interface.NAME: ETH1,
+        Interface.TYPE: InterfaceType.ETHERNET,
+        Interface.STATE: InterfaceState.UP,
+    }
+    iface_state[Interface.IPV4] = create_ipv4_state(enabled=False)
+    iface_state[Interface.IPV6] = create_ipv6_state(
+        enabled=True, dhcp=True, autoconf=False
+    )
+    libnmstate.apply({Interface.KEY: [iface_state]})
+    try:
+        yield iface_state
+    finally:
+        libnmstate.apply(
+            {
+                Interface.KEY: [
+                    {
+                        Interface.NAME: ETH1,
+                        Interface.STATE: InterfaceState.ABSENT,
+                    }
+                ]
+            },
+            verify_change=False,
+        )
+
+
+@pytest.mark.xfail(
+    reason="https://github.com/nmstate/nmstate/issues/736",
+    raises=NmstateVerificationError,
+    strict=True,
+)
+def test_switch_from_dynamic_ip_without_dhcp_srv_to_static_ipv6(
+    eth1_with_dhcp6_no_dhcp_server,
+):
+    iface_state = eth1_with_dhcp6_no_dhcp_server
+    iface_state[Interface.IPV4] = {InterfaceIPv4.ENABLED: False}
+    iface_state[Interface.IPV6] = {
+        InterfaceIPv6.ENABLED: True,
+        InterfaceIPv6.DHCP: False,
+        InterfaceIPv6.AUTOCONF: False,
+        InterfaceIPv6.ADDRESS: [
+            {
+                InterfaceIPv6.ADDRESS_IP: IPV6_ADDRESS2,
+                InterfaceIPv6.ADDRESS_PREFIX_LENGTH: 64,
+            }
+        ],
+    }
+    libnmstate.apply({Interface.KEY: [iface_state]})
+    assertlib.assert_state_match({Interface.KEY: [iface_state]})