title: rake test:units aborted but why?
body: <p>I am currently going through Agile Development With Rails 4th edition (Rails 3.2+). I am trying to preform a unit test the for the "Product" model:</p>
  
  <pre><code>require 'test_helper'
  
  class ProductTest &lt; ActiveSupport::TestCase
     test "product attributes must not be empty" do
      product = Product.new
      assert product.invalid?
      assert product.errors[:title].any?
      assert product.errors[:description].any?
      assert product.errors[:price].any?
      assert product.errors[:image_url].any?
    end
  end
  </code></pre>
  
  <p>This is word for word what the book has, and there is no errata that says otherwise. When I run:</p>
  
  <pre><code>rake test:units
  </code></pre>
  
  <p>I get back the following:</p>
  
  <pre><code>Run options: 
  
  # Running tests:
  
  F
  
  Finished tests in 0.079901s, 12.5155 tests/s, 25.0310 assertions/s.
  
    1) Failure:
  test_product_attributes_must_not_be_empty(ProductTest) [/Users/robertquinn/rails_work/depot/test/unit/product_test.rb:7]:
  Failed assertion, no message given.
  
  1 tests, 2 assertions, 1 failures, 0 errors, 0 skips
  rake aborted!
  Command failed with status (1): [/Users/robertquinn/.rvm/rubies/ruby-1.9.3-...]
  
  Tasks: TOP =&gt; test:units
  (See full trace by running task with --trace)
  Robert-Quinns-MacBook-Pro:depot robertquinn$ 
  </code></pre>
  
  <p>Here are my Product model validations:</p>
  
  <pre><code>class Product &lt; ActiveRecord::Base
    attr_accessible :description, :image_url, :price, :title
  
    validates :description, :image_url, :price, presence: true
    validates :price, numericality: {greater_than_or_equal_to: 0.01}
    validates :title, uniqueness: true
    validates :image_url, allow_blank: true, format: {
      with: %r{\.(gif|jpg|png)$}i,
      message: 'must be a URL for GIF, JPG or PNG image.'
      }
  end
  </code></pre>
  
  <p>I cannot figure out why this rake is being aborted. The test created an empty "Product" object which is thus invalid, and should have errors for every attribute. However, it appears the rake aborts upon hitting the first assertion against the ":title" attribute. I am absolutely clueless here. Any and all input would be appreciated. </p>