def folder(folder = nil, &bl)
      if folder.nil?
        @folder
      else
        folder = folder.is_a?(String) ? @folder/folder : Path(folder)
        raise "Folder `#{folder}` does not exists" unless folder.exists? && folder.directory?
        raise "Folder must be a descendant" unless folder.inside?(@folder)
        child = dup do |c|
          c.parent = self
          c.folder = folder
        end
        yield(child) if block_given?
        @children << child
        child
      end
    end
def folder(folder = nil, &bl)
      if folder.nil?
        @folder
      else
        folder = folder.is_a?(String) ? @folder/folder : Path(folder)
        raise "Folder `#{folder}` does not exists" unless folder.exists? && folder.directory?
        raise "Folder must be a descendant" unless folder.inside?(@folder)
        child = dup do |c|
          c.parent = self
          c.folder = folder
        end
        yield(child) if block_given?
        @children << child
        child
      end
    end
Adds a folder to the list of folders where test case definitions are
 to be found.