Use a schema matcher to capture all entity members

spec/fixtures/api/schemas/public_api/v4/group_labels.json

@@ -0,0 +1,17 @@
+{
+  "type": "array",
+  "items": {
+    "type": "object",
+    "properties" : {
+      "id" : { "type": "integer" },
+      "name" : { "type": "string "},
+      "color" : { "type": "string "},
+      "description" : { "type": "string "},
+      "open_issues_count" : { "type": "integer "},
+      "closed_issues_count" : { "type": "integer "},
+      "open_merge_requests_count" : { "type": "integer "},
+      "subscribed" : { "type": "boolean" }
+    },
+    "additionalProperties": false
+  }
+}

spec/requests/api/group_labels_spec.rb

@@ -14,6 +14,7 @@ describe API::GroupLabels do
       get api("/groups/#{group.id}/labels", user)
 
       expect(response).to have_gitlab_http_status(200)
+      expect(response).to match_response_schema('public_api/v4/group_labels')
       expect(response).to include_pagination_headers
       expect(json_response).to be_an Array
       expect(json_response.size).to eq(2)