Reproduce live migration rollback w/o multi port bindings error

When the libvirt driver does live migration rollback of an instance
with network interfaces, it unconditionally refers to
migrate_data.vifs. These will only be set when Neutron has the
multiple port bindings extension. We don't handle the case of the
extension not being present, and currently the rollback will fail with
a "NotImplementedError: Cannot load 'vifs' in the base class" error.

Related-bug: 1969980
Change-Id: Ieef773453ed9f3ced564c1a352fbefbcc6a653ec

nova/tests/functional/regressions/test_bug_1888395.py

@@ -23,14 +23,8 @@ from nova.tests.fixtures import libvirt as fakelibvirt
 from nova.tests.functional.libvirt import base as libvirt_base
 
 
-class TestLiveMigrationWithoutMultiplePortBindings(
+class TestLiveMigrationWithoutMultiplePortBindingsBase(
         libvirt_base.ServersTestBase):
-    """Regression test for bug 1888395.
-
-    This regression test asserts that Live migration works when
-    neutron does not support the binding-extended api extension
-    and the legacy single port binding workflow is used.
-    """
 
     ADMIN_API = True
     microversion = 'latest'
@@ -72,6 +66,16 @@ class TestLiveMigrationWithoutMultiplePortBindings(
             'nova.tests.fixtures.libvirt.Domain.migrateToURI3',
             self._migrate_stub))
 
+
+class TestLiveMigrationWithoutMultiplePortBindings(
+        TestLiveMigrationWithoutMultiplePortBindingsBase):
+    """Regression test for bug 1888395.
+
+    This regression test asserts that Live migration works when
+    neutron does not support the binding-extended api extension
+    and the legacy single port binding workflow is used.
+    """
+
     def _migrate_stub(self, domain, destination, params, flags):
         """Stub out migrateToURI3."""
 
@@ -124,3 +128,30 @@ class TestLiveMigrationWithoutMultiplePortBindings(
             server, {'OS-EXT-SRV-ATTR:host': 'end_host', 'status': 'ACTIVE'})
         msg = "NotImplementedError: Cannot load 'vif_type' in the base class"
         self.assertNotIn(msg, self.stdlog.logger.output)
+
+
+class TestLiveMigrationRollbackWithoutMultiplePortBindings(
+        TestLiveMigrationWithoutMultiplePortBindingsBase):
+
+    def _migrate_stub(self, domain, destination, params, flags):
+        source = self.computes['start_host']
+        conn = source.driver._host.get_connection()
+        dom = conn.lookupByUUIDString(self.server['id'])
+        dom.fail_job()
+
+    def test_live_migration_rollback(self):
+        self.server = self._create_server(
+            host='start_host',
+            networks=[{'port': self.neutron.port_1['id']}])
+
+        self.assertFalse(
+            self.neutron_api.has_port_binding_extension(self.ctxt))
+        # FIXME(artom) Until bug 1969980 is fixed, this will fail with a
+        # NotImplementedError.
+        self._live_migrate(self.server, migration_expected_state='error',
+                           server_expected_state='ERROR')
+        server = self.api.get_server(self.server['id'])
+        self.assertIn(
+            "NotImplementedError: Cannot load 'vifs' in the base class",
+            server['fault']['details']
+        )