class Rubocop::Cop::Style::Not

This cop checks for uses if the keyword not instead of !.

def on_send(node) 

def on_send(node)
  _receiver, method_name, *args = *node
  # not does not take any arguments
  if args.empty? && method_name == :! &&
      node.loc.selector.is?('not')
    add_offense(node, :selector)
  end
end