! exec karma --config.file=karma.yaml
! stdout .
cmp stderr stderr.txt

-- stderr.txt --
level=ERROR msg="Execution failed" error="valueOnly regex rule '.++++' is invalid: error parsing regexp: invalid nested repetition operator: `++`"
-- karma.yaml --
alertmanager:
  servers:
    - name: default
      uri: https://127.0.0.1:9093
labels:
  valueOnly_re:
    - .++++
