How to define method to be over-ridden in child classes

parent_child.rb

class Parent
  def self.to_be_over_ridden
    raise "Class method `#{__method__}` must be defined in #{name}"
  end

  def to_be_over_ridden
    raise "Instance method `#{__method__}` must be defined in #{self.class.name}"
  end
end

class Child < Parent
  def self.to_be_over_ridden
    puts "Foo"
  end

  def to_be_over_ridden
    puts "Bar"
  end
end

class NaughtyChild < Parent
end

# Outputs: "Bar"
Child.new.to_be_over_ridden

# Outputs: "Foo"
Child.to_be_over_ridden

# Raises error with message "Instance method `to_be_over_ridden` must be defined in NaughtyChild"
begin
  NaughtyChild.new.to_be_over_ridden
rescue => e
  puts e.message
end

# Raises error with message "Class method `to_be_over_ridden` must be defined in NaughtyChild"
begin
  NaughtyChild.to_be_over_ridden
rescue => e
  puts e.message
end