site/docs/layouts/shortcodes/testplan.html

{{ $baseName := .Get 0 }}
{{ $path := path.Join .Site.Params.generatedRoot (printf "%s.testplan" $baseName) }}
{{ if not (fileExists $path) }}
  {{ errorf "Testplan has not been generated for %s" $baseName }}
{{ end }}
{{ readFile $path | safeHTML }}