non_implemented_stack.rb

stack.rb

class LinkedListNode
  attr_accessor :value, :points_to_node

  def initialize(value, points_to_node=nil)
    @value = value
    @points_to_node = points_to_node
  end
end

class Stack
  attr_reader :data
  def initialize
    @data = nil
  end
  def pop
    # Reverse what you did for push
  end
  def push(value)
    # do something using a LinkedListNode
    @data = LinkedListNode.new(value, @data)
  end
end

# -------- You could put what's below in a separate file, but why bother

require 'minitest/autorun'

class TestStack < MiniTest::Unit::TestCase
  def test_pop_without_push_returns_nil
    stack = Stack.new
    assert_equal(nil, stack.pop)
  end

  def test_push_then_pop_returns_what_was_just_pushed
    stack = Stack.new
    stack.push(3)
    assert_equal(3, stack.pop)
  end

  def test_push_a_few_then_pop_a_few
    stack = Stack.new
    stack.push(3)
    stack.push(7)
    stack.push(9)

    puts stack.data.inspect

    assert_equal(9, stack.pop)
    assert_equal(7, stack.pop)
    assert_equal(3, stack.pop)
    assert_equal(nil, stack.pop)
  end

  def test_push_a_few_heterogenous_items_then_pop_a_few
    object = Object.new
    stack = Stack.new
    stack.push(3)
    stack.push(object)
    stack.push(9)
    assert_equal(9, stack.pop)
    assert_equal(object, stack.pop)
    assert_equal(3, stack.pop)
    assert_equal(nil, stack.pop)
  end
end