stubbable.rb

class Stubbable
  def stub(name, block)
    send(:define_singleton_method, name, block)
  end
end

class Class
  def stub(name, block)
    send(:define_singleton_method, name, block)
  end

  def stub_any_instance(name, block)
    ObjectSpace.each_object(self)  do |instance|
      begin
        instance.send(:define_singleton_method, name, block)
      rescue RuntimeError
        next # don't set method on frozen strings
      rescue TypeError
        next # don't set method on numeric types
      end
    end
  end
end

stubby = Stubbable.new

begin
  stubby.foo
rescue NoMethodError => e
  puts e.inspect
end

foo_block = proc { puts 'foo' }
stubby.stub(:foo, foo_block )
stubby.foo

Stubbable.stub('foo', proc { puts 'class foo' })
Stubbable.foo

puts 'Now let\'s put a method on every object'

a = ''
b = {}
c = []
d = Object.new
e = ''

objs = [a, b, c, d, e]

forty_two = proc { puts '42' }
Object.stub_any_instance('print42', forty_two)

objs.each { |obj| obj.print42 }