test-ytt

RESULT

```shell
$ ytt -f template.yaml -f schema.yaml -f value-a.yaml -f value-b.yaml
channels:
  b.atopic:  <===== This should be `a.atopic`
    name: atopic
  b.btopic:
    name: btopic
```

schema.yaml

#@data/values-schema
---
namespace: ""
topics:
- name: ""

template.yaml

#@ load("@ytt:data", "data")
#@ load("@ytt:template", "template")

channels:
  #@ for topic in data.values.topics:
  #@yaml/text-templated-strings
  (@= "{}.{}".format(data.values.namespace, topic.name) @):
    name: #@ topic.name
  #@ end

value-a.yaml

#@data/values
---
namespace: a
topics:
- name: atopic

value-b.yaml

#@data/values
---
namespace: b
topics:
- name: btopic

$ ytt -f template.yaml -f schema.yaml -f value-a.yaml -f value-b.yaml
channels:
  b.atopic:  <===== This should be `a.atopic`
    name: atopic
  b.btopic:
    name: btopic