Use different context for each API request in unit tests

test_router_add_interface_subnet_with_port_from_other_tenant in
neutron.tests.unit.test_l3_plugin.L3NatTestCaseBase was mocking
neutron.context.Context thus performing multiple API requests
with the same context instance. As a context instance also has
a DB session attribute, this might cause unexpected side effects,
especially for plugins which process request asynchronously.

The plugin neutron.plugins.nicira.NeutronServicePlugin was being
affected.

This patch ensures each request has a different context object
without changing the unit test semantics.

It also refactors slightly test_edge_router.py in the nicira
unit test package to avoid executing twice the same unit tests.

Change-Id: I4895faa00ebd915eb9e259930db2d004a9e78a86
Closes-Bug: #1280035

neutron/tests/unit/nicira/test_edge_router.py

@@ -63,19 +63,6 @@ class ServiceRouterTestExtensionManager(object):
         return []
 
 
-class NvpRouterTestCase(test_nicira_plugin.TestNiciraL3NatTestCase):
-
-    def setUp(self, plugin=None, ext_mgr=None, service_plugins=None):
-        plugin = plugin or SERVICE_PLUGIN_NAME
-        # Disable the proxying in the tests but functionality will
-        # be covered separately
-        mock_proxy = mock.patch(
-            "%s.%s" % (SERVICE_PLUGIN_NAME, '_set_create_lswitch_proxy'))
-        mock_proxy.start()
-        super(NvpRouterTestCase, self).setUp(plugin=plugin, ext_mgr=ext_mgr,
-                                             service_plugins=service_plugins)
-
-
 class ServiceRouterTest(test_nicira_plugin.NiciraL3NatTest,
                         test_l3_plugin.L3NatTestCaseMixin):
 
@@ -169,7 +156,8 @@ class ServiceRouterTest(test_nicira_plugin.NiciraL3NatTest,
         return router_req.get_response(self.ext_api)
 
 
-class ServiceRouterTestCase(ServiceRouterTest, NvpRouterTestCase):
+class ServiceRouterTestCase(ServiceRouterTest,
+                            test_nicira_plugin.TestNiciraL3NatTestCase):
 
     def test_router_create(self):
         name = 'router1'

neutron/tests/unit/test_l3_plugin.py

@@ -379,7 +379,8 @@ class L3NatTestCaseMixin(object):
 
     def _router_interface_action(self, action, router_id, subnet_id, port_id,
                                  expected_code=exc.HTTPOk.code,
-                                 expected_body=None):
+                                 expected_body=None,
+                                 tenant_id=None):
         interface_data = {}
         if subnet_id:
             interface_data.update({'subnet_id': subnet_id})
@@ -388,6 +389,10 @@ class L3NatTestCaseMixin(object):
 
         req = self.new_action_request('routers', interface_data, router_id,
                                       "%s_router_interface" % action)
+        # if tenant_id was specified, create a tenant context for this request
+        if tenant_id:
+            req.environ['neutron.context'] = context.Context(
+                '', tenant_id)
         res = req.get_response(self.ext_api)
         self.assertEqual(res.status_int, expected_code)
         response = self.deserialize(self.fmt, res)
@@ -734,10 +739,6 @@ class L3NatTestCaseBase(L3NatTestCaseMixin):
     def test_router_add_interface_subnet_with_port_from_other_tenant(self):
         tenant_id = _uuid()
         other_tenant_id = _uuid()
-        tenant_context = context.Context(user_id=None, tenant_id=tenant_id)
-        admin_context = context.get_admin_context()
-        with mock.patch('neutron.context.Context') as ctx:
-            ctx.return_value = admin_context
         with contextlib.nested(
             self.router(tenant_id=tenant_id),
             self.network(tenant_id=tenant_id),
@@ -745,26 +746,25 @@ class L3NatTestCaseBase(L3NatTestCaseMixin):
             with contextlib.nested(
                 self.subnet(network=n1, cidr='10.0.0.0/24'),
                 self.subnet(network=n2, cidr='10.1.0.0/24')) as (s1, s2):
-                        ctx.return_value = admin_context
                     body = self._router_interface_action(
                         'add',
                         r['router']['id'],
                         s2['subnet']['id'],
                         None)
                     self.assertIn('port_id', body)
-                        ctx.return_value = tenant_context
                     self._router_interface_action(
                         'add',
                         r['router']['id'],
                         s1['subnet']['id'],
-                            None)
+                        None,
+                        tenant_id=tenant_id)
                     self.assertIn('port_id', body)
                     self._router_interface_action(
                         'remove',
                         r['router']['id'],
                         s1['subnet']['id'],
-                            None)
+                        None,
-                        ctx.return_value = admin_context
+                        tenant_id=tenant_id)
                     body = self._router_interface_action(
                         'remove',
                         r['router']['id'],