Question

Book has_many Reviews和Review belongs_to Book。我使用的是rails 4.0和ruby 2.0.0p247

我按如下方式运行测试：

test "DELETE destroy should decrement review count by 1" do

    book = Book.create({
                         :isbn=>"1234567890",
                         :title=>"Dummies Guide to Rails",
                         :author=>"KP",
                         :description=>"lorem ipsum"
    })

    # assert_not_nil Book.find_by_isbn('1234567890')

    review = Review.create!({
                              :book_id => book.id,
                              :name => "KP",
                              :email => "KP@KP.com",
                              :description => "Good book.",
                              # :book => book
    })

    assert_difference 'Review.count', 1 , "a review should be deleted" do
      puts Review.count # => 3
      delete :destroy, :book_id => book.id, :id => review.id
      assert_response :redirect
      puts Review.count # => 2
    end
    # puts Review.count
    assert_nil Review.find_by_id(review.id)
  end

正如您所看到的，我在删除与书籍相关的评论之前和之后打印了计数，并且它减少了1.但是，断言期望并收到不正确的计数，将其显示为错误：

 1) Failure:
ReviewsControllerTest#test_DELETE_destroy_should_decrement_review_count_by_1 [test/controllers/reviews_controller_test.rb:56]:
a review should be deleted.
"Review.count" didn't change by 1.
Expected: 4
  Actual: 2

我放弃了数据库并开始使用空白数据库。我有两个问题：

我只创建了一本与一本书相关的评论。为什么Review.count打印3和2与1和0相对应？
为什么断言期望4，但收到2？

感谢。

Answer 1

此行表示您期望Plus 1（1或+1）的差异。

assert_difference 'Review.count', 1 , "a review should be deleted"

但实际上你想要负一（-1）的差异，所以你应该写

assert_difference 'Review.count', -1 , "a review should be deleted"

如需更多指南，请访问assert_difference

Answer 2

你有3条记录。如果你写assert_difference 'Review.count', 1 ...它最后会有4个。但是如果你写assert_difference 'Review.count', -1 ...它预期2，因此减少1。

assert_difference期望错误计数，因此失败

2 个答案: