use type instead of struct literal in unit test
diff --git a/openstack/blockstorage/v2/volumes/testing/requests_test.go b/openstack/blockstorage/v2/volumes/testing/requests_test.go
index 0385e50..05fd686 100644
--- a/openstack/blockstorage/v2/volumes/testing/requests_test.go
+++ b/openstack/blockstorage/v2/volumes/testing/requests_test.go
@@ -109,10 +109,7 @@
 	allPages, err := volumes.List(client.ServiceClient(), &volumes.ListOpts{}).AllPages()
 	th.AssertNoErr(t, err)
 
-	var actual []struct {
-		volumes.Volume
-		tenantattr.VolumeExt
-	}
+	var actual []VolumeWithExt
 	err = volumes.ExtractVolumesInto(allPages, &actual)
 	th.AssertNoErr(t, err)
 	th.AssertEquals(t, 2, len(actual))