1. code.rb

class Object
  def self.typecheck(object)
    unless self == object.class
      raise ArgumentError,
        "expected type: #{self}. given: #{object.class}."
    end
  end
end

class Foo; end
class Bar; end

def my_method(arg1, arg2)
  Foo.typecheck arg1
  Bar.typecheck arg2

  puts "The method finished!"
end

puts "1..."
my_method(Foo.new, Bar.new)
puts "2..."
my_method("hi.", Bar.new)

2. output.txt

1...
The method finished!
2...
driver.rb:4:in `typecheck': expected type: Foo. given: String. (ArgumentError)
  from driver.rb:14:in `my_method'
	from driver.rb:23:in `<main>'