require 'stack'

describe Stack do

  before do
    @stack = Stack.new
  end

  it 'should be empty' do
    @stack.should be_empty
  end

  it 'should have no element on top' do
    lambda { @stack.top }.should raise_error(Test::Unit::AssertionFailedError)
  end

  it 'should not be possible to pop an element' do
    lambda { @stack.pop }.should raise_error(Stack::NoPopForEmptyStack)
  end

  it 'a pushed element should be on the top' do
    element = 0
    @stack.push(element)
    @stack.should_not be_empty
    @stack.top.should be_equal(element)
    @stack.pop.should be_equal(element)
    @stack.should be_empty
  end

end