method_defined.rb

class Mom
  class << self
    def defined_it?
      method_defined? :the_method
    end
  end
end

class Son < Mom
  class << self
    def the_method
      puts "definition!"
    end
  end
end

puts Mom.defined_it? # false
puts Son.defined_it? # false

respond_to.rb

class Mom
  class << self
    def defined_it?
      respond_to? :the_method
    end
  end
end

class Son < Mom
  class << self
    def the_method
      puts "definition!"
    end
  end
end

puts Mom.defined_it? # false
puts Son.defined_it? # true