class Rubocop::Cop::Style::ModuleFunction

end
…
extend self
module Test
@example
This cops checks for use of ‘extend self` in a module.

def on_module(node) 

def on_module(node)
  _name, body = *node
  if body && body.type == :begin
    body.children.each do |body_node|
      if body_node == TARGET_NODE
        add_offence(:convention, body_node.loc.expression, MSG)
      end
    end
  end
end