adder.rb

class Adder
  def initialize(*args)
    @args = args
    @block = lambda {|*args|
      args.inject(0) {|a, sum| sum += a}
    }
  end
  
  def add
    instance_exec(*@args, &@block)
  end
end

gistfile2.txt

# Failure for the 3rd spec in ie_spec.rb and test in ie_test.rb is the same:

wrong # of arguments(4 for 3)

ie_spec.rb

require 'adder'

describe "instance_exec" do
  it "works with two args" do
    adder = Adder.new(1,2)
    adder.add.should == 3
  end

  it "works with three args" do
    adder = Adder.new(1,2,3)
    adder.add.should == 6
  end

  it "fails with four args" do
    adder = Adder.new(1,2,3,4)
    adder.add.should == 10
  end
end

ie_test.rb

require 'adder'
require 'test/unit'

class InstanceExecTest < Test::Unit::TestCase
  def test_with_two_args
    adder = Adder.new(1,2)
    assert_equal 3, adder.add
  end
  
  def test_with_three_args
    adder = Adder.new(1,2,3)
    assert_equal 6, adder.add
  end
  
  def test_with_four_args
    adder = Adder.new(1,2,3,4)
    assert_equal 10, adder.add
  end
end