def whitelist_file(file)
      file = Regexp.new(file) unless file.kind_of?(Regexp)
      whitelist_files << file
      whitelist_files.dup
    end
def whitelist_file(file)
      file = Regexp.new(file) unless file.kind_of?(Regexp)
      whitelist_files << file
      whitelist_files.dup
    end
Add a file to the healthcheck whitelist.

 @example
   whitelist_file '/path/to/file'

 @param [String, Regexp] file
   the name of a file to ignore in the healthcheck

 @return [Array<String>]
   the list of currently whitelisted files