This is based on the existing `helm-local` test.

This is based on the existing `yaml-test` test.

The invoke used for Kustomize was already fixed to be resilient to `None` or empty dicts being returned in a907bdd. This test, which is based on the existing `kustomize` test is to ensure it continues to work without an error being raised.

Make the hand-rolled invoke code resilient to `invoke` returning either `None` or an empty dict for empty results. This aligns all invokes with the same pattern as introduced by a907bdd.