gistfile1.rb

class MiniTest::Unit::TestCase
  def assert_change(block)
    before = block.call

    yield

    refute_equal before, block.call
  end

  def refute_change(block)
    before = block.call

    yield

    assert_equal before, block.call
  end
end

assert_change(lambda { @deck.cards.first }) { @deck.cut! }