Add test for showing volume metadata item

This patch adds test for the missing API (volume v2):
show specific metadata item for a volume.

Including:

[1] Add show volume metadata item API to v2 volumes_client
[2] Add unit test for the API
[3] Modify test case: test_update_volume_metadata_item
[4] Add release note

According defcore(interop) patch is:
Ica8b57f5f5392e2bf47e368e9b10ef9fa5695c30

Change-Id: Idb9d198383ce93453707f1204806e4ae82c1e46a

releasenotes/notes/add-show-volume-metadata-item-api-to-v2-volumes-client-47d59ecd999ca9df.yaml

@@ -0,0 +1,6 @@
+---
+features:
+  - |
+    Add show volume metadata item API to v2 volumes_client library.
+    This feature enables the possibility to show a volume's metadata for
+    a specific key.

tempest/api/volume/test_volume_metadata.py

@@ -70,7 +70,7 @@ class VolumesMetadataTest(base.BaseVolumeTest):
                         'Delete one item metadata of the volume failed')
 
     @decorators.idempotent_id('862261c5-8df4-475a-8c21-946e50e36a20')
-    def test_update_volume_metadata_item(self):
+    def test_update_show_volume_metadata_item(self):
         # Update metadata item for the volume
         metadata = {"key1": "value1",
                     "key2": "value2",
@@ -88,6 +88,12 @@ class VolumesMetadataTest(base.BaseVolumeTest):
         body = self.volumes_client.update_volume_metadata_item(
             self.volume['id'], "key3", update_item)['meta']
         self.assertEqual(update_item, body)
+
+        # Get a specific metadata item of the volume
+        body = self.volumes_client.show_volume_metadata_item(
+            self.volume['id'], "key3")['meta']
+        self.assertEqual({"key3": expect['key3']}, body)
+
         # Get the metadata of the volume
         body = self.volumes_client.show_volume_metadata(
             self.volume['id'])['metadata']

tempest/lib/services/volume/v2/volumes_client.py

@@ -283,6 +283,14 @@ class VolumesClient(rest_client.RestClient):
         self.expected_success(200, resp.status)
         return rest_client.ResponseBody(resp, body)
 
+    def show_volume_metadata_item(self, volume_id, id):
+        """Show metadata item for the volume."""
+        url = "volumes/%s/metadata/%s" % (volume_id, id)
+        resp, body = self.get(url)
+        body = json.loads(body)
+        self.expected_success(200, resp.status)
+        return rest_client.ResponseBody(resp, body)
+
     def update_volume_metadata_item(self, volume_id, id, meta_item):
         """Update metadata item for the volume."""
         put_body = json.dumps({'meta': meta_item})

tempest/tests/lib/services/volume/v2/test_volumes_client.py

@@ -20,6 +20,12 @@ from tempest.tests.lib.services import base
 
 class TestVolumesClient(base.BaseServiceTest):
 
+    FAKE_VOLUME_METADATA_ITEM = {
+        "meta": {
+            "key1": "value1"
+        }
+    }
+
     def setUp(self):
         super(TestVolumesClient, self).setUp()
         fake_auth = fake_auth_provider.FakeAuthProvider()
@@ -45,8 +51,23 @@ class TestVolumesClient(base.BaseServiceTest):
             **kwargs
         )
 
+    def _test_show_volume_metadata_item(self, bytes_body=False):
+        self.check_service_client_function(
+            self.client.show_volume_metadata_item,
+            'tempest.lib.common.rest_client.RestClient.get',
+            self.FAKE_VOLUME_METADATA_ITEM,
+            to_utf=bytes_body,
+            volume_id="a3be971b-8de5-4bdf-bdb8-3d8eb0fb69f8",
+            id="key1")
+
     def test_force_detach_volume_with_str_body(self):
         self._test_force_detach_volume()
 
     def test_force_detach_volume_with_bytes_body(self):
         self._test_force_detach_volume(bytes_body=True)
+
+    def test_show_volume_metadata_item_with_str_body(self):
+        self._test_show_volume_metadata_item()
+
+    def test_show_volume_metadata_item_with_bytes_body(self):
+        self._test_show_volume_metadata_item(bytes_body=True)