def validate_file_contains_plugin!(file)
      plugin_count_was = Danger::Plugin.all_plugins.length
      yield

      if Danger::Plugin.all_plugins.length == plugin_count_was
        raise("#{file} doesn't contain any valid danger plugins.")
      end
    end
def validate_file_contains_plugin!(file)
      plugin_count_was = Danger::Plugin.all_plugins.length
      yield

      if Danger::Plugin.all_plugins.length == plugin_count_was
        raise("#{file} doesn't contain any valid danger plugins.")
      end
    end
Raises an error when the given block does not register a plugin.