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

#@ def tpl():
test3: first
test4: second
#@ end

test3: first
_: #@ template.replace(tpl())

+++

ERR: 
- template.replace: expected key 'test3' to not be specified again (unless 'yaml/map-key-override' annotation is added)
    in <toplevel>
      stdin:9 | _: #@ template.replace(tpl())