Unexpected failure running tests pg 85-89

First time RoR developer, working through 4th edition with Rails 3.2.1 and Ruby 1.9.3 on a Windows 7 installation.
When I run rake test:units I get one unexpected failure, always on the first item in the OK array (regardless of which element is first):

Finished tests in 0.569033s, 8.7868 tests/s, 26.3605 assertions/s.

  1) Failure:
test_image_URL(ProductTest) [C:/Sites/depot/test/unit/product_test.rb:73]:
fred2.jpg shouldn't be invalid

5 tests, 15 assertions, 1 failures, 0 errors, 0 skips

Here’s my product_test.rb:

require 'test_helper'

class ProductTest < ActiveSupport::TestCase
  fixtures :products

  def new_product(image_url)
    Product.new(
        title:            "whatever",
        description:    "whatever",
        image_url:        image_url,
        price: 14.99
    )
  end
  test "image URL" do
    ok = %w{ fred2.jpg fred1.GIF jones.gif fred3.png FRED4.JPG FRED5.Jpg http://a.b.c/x/y/z/fred6.gif }
    bad = %w{ fred7.doc fred8.gif/more fred9.gif.more }

    ok.each do |name|
        assert new_product(name).valid?, "#{name} shouldn't be invalid" 
    end
    bad.each do |name|
        assert new_product(name).invalid?, "#{name} shouldn't be valid" 
    end
  end
end

and here’s my product.rb:

class Product < ActiveRecord::Base
    validates :title, :description, :image_url, presence: true
    validates :price, numericality: {greater_than_or_equal_to: 0.01}
    validates :title, uniqueness:true
    validates :description, :length => {:minimum => 10}
    validates :image_url, allow_blank: true, format: {
        with:  %r{\.(jpg|gif|png)$}i, 
        message: 'must be a URL for GIF, JPG, or PNG image.'
    }
end

I’ve restarted the server (no change), rearranged the validations in product.rb (no change),
stripped all other tests from product_test.rb (as shown above),
rearranged the items in the OK array, played with the spacing of the %w{} construct…
still get failure of first element in the OK array. According to everything I’ve read, this should work… scratching my now-bald head (after pulling all my hair out!)
Any ideas? Thanks in advance!

Update: rewrote the OK array as:

    ok = ["jones.gif","fred2.jpg","fred1.GIF","fred3.png","FRED4.JPG","FRED5.Jpg","http://a.b.c/x/y/z/fred6.gif"]

with the same results; Failure of first entry jones.gif. Hmmmm….

The issue is with
validates :description, :length => {:minimum => 10}

Your description is ‘Whatever’ and thus 8 characters long. It fails on creating that record, not on the image url.