mocking_new.rb

require 'test/unit'
require 'rubygems'
require 'mocha'

class Class1
  def foo
    c2 = Class2.new
    x = c2.bar
    c2.baz(x)
  end
end

class Class2
  def bar
    21
  end
  def baz(x)
    x * 2
  end
end

class MyTest < Test::Unit::TestCase
  def test_foo
    n = 99
    c2 = mock()
    Class2.expects(:new).returns(c2)
    c2.expects(:bar).returns(n)
    c2.expects(:baz).with(n).returns(1)
    assert_equal 1, Class1.new.foo
  end
end