以前的随笔都是按照书上的例子写下来的，但是，这次在测试Model时，按照书上的例子代码怎么也走不通，所以就换个方式，这篇变成了提问。
按照书上的说法，在products_test.rb开始的时候，会根据定义的yml文件，加载测试数据到一个Hash里，这样，在test的时候我们就可以根据yml文件中用例的名字来访问一个product对象，例如：
def test_read_with_hash
assert_kind_of Product, @product
vc_book = @products["version_control_book"]
assert_equal vc_book["id"], @product.id
assert_equal vc_book["title"], @product.title
assert_equal vc_book["description"], @product.description
assert_equal vc_book["image_url"], @product.image_url
assert_equal vc_book["price"], @product.price
assert_equal vc_book["date_available"], @product.date_available_before_type_cast
end
但是，根据在运行测试的时候总是提示vc_book为Null的错误：
3) Error:
test_read_with_hash(ProductTest):
NoMethodError: You have a nil object when you didn't expect it!
You might have expected an instance of Array.
The error occurred while evaluating nil.[]
test/unit/product_test.rb:41:in `test_read_with_hash'
怎么回事呢？即使将product_test.rb里的内容全部替换成书中完整的代码也还是不行，是不是版本问题？
附product_test.rb全部代码：
require File.dirname(__FILE__) + '/../test_helper'
class ProductTest < Test::Unit::TestCase
fixtures :products
def setup
@product = Product.find(1)
end
# Replace this with your real tests.
def test_truth
assert_kind_of Product, @product
end
def test_create
assert_kind_of Product, @product
assert_equal 1, @product.id
assert_equal "Pragmatic Version Control", @product.title
assert_equal "How to use version control", @product.description
assert_equal "http://.../sk_svn_small.jpg", @product.image_url
assert_equal 29.95, @product.price
assert_equal "2005-01-26 00:00:00",
@product.date_available_before_type_cast
end
def test_update
assert_equal 29.95, @product.price
@product.price = 99.99
assert @product.save, @product.errors.full_messages.join("; ")
@product.reload
assert_equal 99.99, @product.price
end
#~ def test_destroy
#~ @product.destroy
#~ assert_raise(ActiveRecord::RecordNotFound) { Product.find(@product.id) }
#~ end
def test_validate
assert_equal 29.95, @product.price
@product.price = 0.00
assert !@product.save
assert_equal 1, @product.errors.count
assert_equal "should be positive", @product.errors.on(:price)
end
def test_read_with_hash
assert_kind_of Product, @product
vc_book = @products["version_control_book"]
assert_equal vc_book["id"], @product.id
assert_equal vc_book["title"], @product.title
assert_equal vc_book["description"], @product.description
assert_equal vc_book["image_url"], @product.image_url
assert_equal vc_book["price"], @product.price
assert_equal vc_book["date_available"], @product.date_available_before_type_cast
end
def test_read_with_fixture_variable
assert_kind_of Product, @product
assert_equal @version_control_book.id, @product.id
assert_equal @version_control_book.title, @product.title
assert_equal @version_control_book.description, @product.description
assert_equal @version_control_book.image_url, @product.image_url
assert_equal @version_control_book.price, @product.price
assert_equal @version_control_book.date_available, @product.date_available
end
end