Writing assertion without modifying target using an overlay.

assert-has-resource-meow.yaml

#@ load("@ytt:overlay", "overlay")

#@overlay/match by=overlay.subset({"kind": "ClusterRole", "metadata":{"name":"my-meow"}})
---
rules:
#@overlay/match by=overlay.all
-
  #@overlay/assert via=lambda given,expects: (given[0]==expects[0], "Given '{}', expects '{}'".format(given[0],expects[0]))
  resourceNames:
  #@overlay/match by=overlay.all
  - "meow"

good-cluster-role.yaml

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: my-meow
rules:
- apiGroups:
  - cat.meow.io
  resourceNames:
  - meow
  resources:
  - meowResource
  verbs:
  - use