ruby-on-rails - Rails 的 assert_difference 是否忽略了一些变化？

Question

我有一个测试，我在其中完成了对拥有一个帐户的用户的付款。该帐户包含余额并有许多交易。

付款完成后，将创建交易并更新帐户余额。

使用 assert_difference 检查交易数量的变化给出了预期的结果。但是，使用 assert_difference 来检查余额是否已更改不会。我可以在我的日志中看到更新余额的 SQL，但断言认为它没有改变。

我完全糊涂了，谁能解释一下？

提前致谢。

这通过了:

assert_difference("a_user.account.transactions.count", 1) do
  # Process payment
end

这失败了，说没有变化:

assert_difference("a_user.account.balance", 250.00) do
  # Process payment
end

这是来自断言的失败消息:

"a_user.account.balance" didn't change by 250.0.
<300.0> expected but was
<50.0>.

这是日志文件中的相关 SQL:

  User Load (0.4ms)   SELECT * FROM `users` WHERE (`users`.`id` = 108093344) 
  Account Load (0.2ms)   SELECT * FROM `accounts` WHERE (`accounts`.user_id = 108093344) LIMIT 1
  Transaction Columns (1.5ms)   SHOW FIELDS FROM `transactions`
  Transaction Create (0.3ms)   INSERT INTO `transactions` (`created_at`, `updated_at`, `amount`, `account_id`, `detail`) VALUES('2011-02-01 17:15:21', '2011-02-01 17:15:21', 250.0, 956948796, 'Payment completed')
  Account Load (0.2ms)   SELECT * FROM `accounts` WHERE (`accounts`.`id` = 956948796) 
  Account Update (0.2ms)   UPDATE `accounts` SET `updated_at` = '2011-02-01 17:15:21', `balance` = 300.0 WHERE `id` = 956948796

Answer 1

尝试重新加载记录

assert_difference("a_user.account.reload.balance", 250.00) do
  # Process payment
end