Problem with using before(:all) in a view spec

show.html.erb_spec.rb

require 'spec_helper'

describe "carts/show" do
  # using before(:all) rather than before(:each) causes the error:
  # NoMethodError: undefined method `example_group' for nil:NilClass
  # ~/.rvm/gems/ruby-1.9.3-p125/gems/rspec-rails-2.12.0/lib/rspec/rails/example/view_example_group.rb:106:in `_default_file_to_render'
  # ~/.rvm/gems/ruby-1.9.3-p125/gems/rspec-rails-2.12.0/lib/rspec/rails/example/view_example_group.rb:112:in `_default_render_options'
  # ~/.rvm/gems/ruby-1.9.3-p125/gems/rspec-rails-2.12.0/lib/rspec/rails/example/view_example_group.rb:45:in `render'
  # show.html.erb_spec.rb:10:in `block (2 levels) in <top (required)>'
  before(:each) do
    book = build_stubbed(:product, title: "book")
    car = build_stubbed(:product, title: "car")
    line_item1 = build_stubbed(:line_item, product: book, quantity: 3)
    line_item2 = build_stubbed(:line_item, product: car, quantity: 1)
    @cart = assign(:cart, build_stubbed(:cart, line_items: [line_item1, line_item2]))
    render
  end

  it "displays a single car" do
    assert_select "li", text: "1 time: car"
  end
  it "displays 3 books" do
    assert_select "li", text: "3 times: book"
  end
  it "has exactly 2 items" do
    assert_select "li", 2
  end

end