编译时出错(Error during compile)

 在技​​术上测试与数据库（nosql或其他）的通信不是单元测试 ，因为测试正在测试与外部系统的交互，而不仅仅是测试隔离的代码单元。 然而，与数据库通信的测试通常是非常有用的，并且通常足够快以与其他单元测试一起运行。 
 
 通常我有一个服务接口（例如UserService），它封装了处理数据库的所有逻辑。 依赖于UserService的代码可以使用嘲弄的UserService版本，并且易于测试。 
 
 当测试与Mongo谈话的服务（例如MongoUserService）的实现时，最简单的方法是编写一些将在本地机器上启动/停止mongo进程的java代码，并让您的MongoUserService与之连接，看到这个问题笔记 。 
 
 您可以尝试在测试MongoUserService时嘲笑数据库的功能，但通常这样做太容易出错，并且不会测试您真正想要测试的内容，即与实际数据库的交互。 所以在为MongoUserService编写测试时，您将为每个测试设置一个数据库状态。 看一下DbUnit，为一个使用数据库这样做的框架的例子。 

As sbridges wrote in this post it is a bad idea not to have a dedicated service (sometimes also known as repository or DAO) which abstracts the data access from the logic. Then you could test the logic by providing a mock of the DAO.
 
Another approach which I do is to create a Mock of the Mongo object (e.g. PowerMockito) and then return the appropriate results. This because you don't have to test if the database works in unit tests but more over you should test if the right query was sent to the databse.
 
Mongo mongo = PowerMockito.mock(Mongo.class);
DB db = PowerMockito.mock(DB.class);
DBCollection dbCollection = PowerMockito.mock(DBCollection.class);

PowerMockito.when(mongo.getDB("foo")).thenReturn(db);
PowerMockito.when(db.getCollection("bar")).thenReturn(dbCollection);

MyService svc = new MyService(mongo); // Use some kind of dependency injection
svc.getObjectById(1);

PowerMockito.verify(dbCollection).findOne(new BasicDBObject("_id", 1));
 
That would also be an option. Of course the creation of the mocks and returning of the appropriate objects is just coded as an example above.