Testing can be simplified if you can get your database in a known state before a test is run.A database should only be used for one test at a time;otherwise the database state cannot be guarantied.

• 让你的数据库在测试运行之前处于一个已知状态可以简化测试.；一个数据库在同一时间应该只用于一个测试；否则数据库状态无法保障