Add test for showing snapshot metadata item

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

Including:

[1] Add show snapshot metadata item API to v2 snapshots_client
[2] Add unit test for the API
[3] Modify test case: test_update_snapshot_metadata_item
[4] Add release note

According defcore(interop) patch is:
I672bbcb9983e7a3ace7769722d6ff97f7bc0ccc8

Change-Id: I3697406e5541bbdb191e4d6e63831be31b471e78

releasenotes/notes/add-show-snapshot-metadata-item-api-to-v2-snapshots-client-bd3cbab3c7f0e0b3.yaml

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

tempest/api/volume/test_snapshot_metadata.py

@@ -81,7 +81,7 @@ class SnapshotMetadataTestJSON(base.BaseVolumeTest):
         self.assertNotIn("key3", body)
 
     @decorators.idempotent_id('e8ff85c5-8f97-477f-806a-3ac364a949ed')
-    def test_update_snapshot_metadata_item(self):
+    def test_update_show_snapshot_metadata_item(self):
         # Update metadata item for the snapshot
         metadata = {"key1": "value1",
                     "key2": "value2",
@@ -101,6 +101,12 @@ class SnapshotMetadataTestJSON(base.BaseVolumeTest):
         body = self.snapshots_client.update_snapshot_metadata_item(
             self.snapshot['id'], "key3", meta=update_item)['meta']
         self.assertEqual(update_item, body)
+
+        # Get a specific metadata item of the snapshot
+        body = self.snapshots_client.show_snapshot_metadata_item(
+            self.snapshot['id'], "key3")['meta']
+        self.assertEqual({"key3": expect['key3']}, body)
+
         # Get the metadata of the snapshot
         body = self.snapshots_client.show_snapshot_metadata(
             self.snapshot['id'])['metadata']

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

@@ -164,6 +164,14 @@ class SnapshotsClient(rest_client.RestClient):
         self.expected_success(200, resp.status)
         return rest_client.ResponseBody(resp, body)
 
+    def show_snapshot_metadata_item(self, snapshot_id, id):
+        """Show metadata item for the snapshot."""
+        url = "snapshots/%s/metadata/%s" % (snapshot_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_snapshot_metadata_item(self, snapshot_id, id, **kwargs):
         """Update metadata item for the snapshot."""
         # TODO(piyush): Current api-site doesn't contain this API description.

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

@@ -72,6 +72,12 @@ class TestSnapshotsClient(base.BaseServiceTest):
         ]
     }
 
+    FAKE_SNAPSHOT_METADATA_ITEM = {
+        "meta": {
+            "key1": "value1"
+        }
+    }
+
     def setUp(self):
         super(TestSnapshotsClient, self).setUp()
         fake_auth = fake_auth_provider.FakeAuthProvider()
@@ -142,6 +148,15 @@ class TestSnapshotsClient(base.BaseServiceTest):
             self.FAKE_INFO_SNAPSHOT,
             bytes_body, volume_type_id="cbc36478b0bd8e67e89")
 
+    def _test_show_snapshot_metadata_item(self, bytes_body=False):
+        self.check_service_client_function(
+            self.client.show_snapshot_metadata_item,
+            'tempest.lib.common.rest_client.RestClient.get',
+            self.FAKE_SNAPSHOT_METADATA_ITEM,
+            bytes_body,
+            snapshot_id="3fbbcccf-d058-4502-8844-6feeffdf4cb5",
+            id="key1")
+
     def test_create_snapshot_with_str_body(self):
         self._test_create_snapshot()
 
@@ -184,6 +199,12 @@ class TestSnapshotsClient(base.BaseServiceTest):
     def test_update_snapshot_metadata_with_bytes_body(self):
         self._test_update_snapshot_metadata(bytes_body=True)
 
+    def test_show_snapshot_metadata_item_with_str_body(self):
+        self._test_show_snapshot_metadata_item()
+
+    def test_show_snapshot_metadata_item_with_bytes_body(self):
+        self._test_show_snapshot_metadata_item(bytes_body=True)
+
     def test_force_delete_snapshot(self):
         self.check_service_client_function(
             self.client.force_delete_snapshot,