Add functional regression recreate test for bug 1825020

Change I06fad233006c7bab14749a51ffa226c3801f951b in Stein
started validating extra specs on the new flavor during a
resize but didn't take into account some validation that
happens with disk size with the new flavor if the validation
code isn't told that the server is volume-backed. That results
in a 500 FlavorDiskSmallerThanMinDisk response from the API
if the new flavor has a smaller disk size than the current
flavor that the server is using, which shouldn't actually
matter for a volume-backed server.

This adds a functional regression test to recreate the bug.

Change-Id: I9e7e44727946705506d740896349ca1833cfddcd
Related-Bug: #1825020
(cherry picked from commit a40c7f3e8d)

nova/tests/functional/regressions/test_bug_1825020.py

@@ -0,0 +1,82 @@
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+
+import six
+
+from nova import test
+from nova.tests import fixtures as nova_fixtures
+from nova.tests.functional.api import client as api_client
+from nova.tests.functional import fixtures as func_fixtures
+from nova.tests.functional import integrated_helpers
+from nova.tests.unit.image import fake as fake_image
+
+
+class VolumeBackedResizeDiskDown(test.TestCase,
+                                 integrated_helpers.InstanceHelperMixin):
+    """Regression test for bug 1825020 introduced in Stein.
+
+    This tests a resize scenario where a volume-backed server is resized
+    to a flavor with a smaller disk than the flavor used to create the
+    server. Since the server is volume-backed, the disk in the new flavor
+    should not matter since it won't be used for the guest.
+    """
+
+    def setUp(self):
+        super(VolumeBackedResizeDiskDown, self).setUp()
+        self.flags(allow_resize_to_same_host=True)
+
+        api_fixture = self.useFixture(nova_fixtures.OSAPIFixture(
+            api_version='v2.1'))
+        self.api = api_fixture.admin_api
+
+        self.useFixture(nova_fixtures.NeutronFixture(self))
+        self.useFixture(nova_fixtures.CinderFixtureNewAttachFlow(self))
+        self.useFixture(func_fixtures.PlacementFixture())
+        fake_image.stub_out_image_service(self)
+        self.addCleanup(fake_image.FakeImageService_reset)
+
+        self.start_service('conductor')
+        self.start_service('scheduler')
+        self.start_service('compute')
+
+    def test_volume_backed_resize_disk_down(self):
+        # First determine the flavors we're going to use by picking two flavors
+        # with different size disks and create a volume-backed server using the
+        # flavor with the bigger disk size.
+        flavors = self.api.get_flavors()
+        flavor1 = flavors[0]
+        flavor2 = flavors[1]
+        self.assertGreater(flavor2['disk'], flavor1['disk'])
+
+        vol_id = nova_fixtures.CinderFixtureNewAttachFlow.IMAGE_BACKED_VOL
+        server = {
+            'name': 'test_volume_backed_resize_disk_down',
+            'imageRef': '',
+            'flavorRef': flavor2['id'],
+            'block_device_mapping_v2': [{
+                'source_type': 'volume',
+                'destination_type': 'volume',
+                'boot_index': 0,
+                'uuid': vol_id
+            }]
+        }
+        server = self.api.post_server({'server': server})
+        self._wait_for_state_change(self.api, server, 'ACTIVE')
+
+        # Now try to resize the server with the flavor that has smaller disk.
+        data = {'resize': {'flavorRef': flavor1['id']}}
+        # FIXME(mriedem): This will raise FlavorDiskSmallerThanMinDisk as a 500
+        # error until bug 1825020 is fixed.
+        ex = self.assertRaises(api_client.OpenStackApiException,
+                               self.api.post_server_action, server['id'], data)
+        self.assertEqual(500, ex.response.status_code)
+        self.assertIn('FlavorDiskSmallerThanMinDisk', six.text_type(ex))