PowerMockito测试MongoClient单例

Question

我有一个带有静态方法的惰性单例MongoConnection类，该静态方法返回MongoConnection.getClient()上的MongoClient实例：

 public class MongoConnection {

    private static MongoClient mongoclient;

    private MongoConnection() {

    }

    public static MongoClient getClient() {
        if (mongoclient == null) {
            // code to initialize MongoClient
        }
        return mongoclient;
    }
}

我如何使用PowerMockito模拟MongoConnection单例并测试GetClient方法。

我没有选择singleton，因为应用程序中只有MongoClient的单个实例（根据MongoDB文档）。

谢谢你

Answer 1

下面的示例演示如何将Mockito与PowerMockito一起使用来模拟MongoConnection.getMongoClient():

@RunWith(PowerMockRunner.class)
@PrepareForTest({MongoConnection.class})
public class ATest {

    @Test
    public void aTestWhichRequiresMockingMongoConnection() {
        MongoClient mongoClient = Mockito.mock(MongoClient.class);
        PowerMockito.mockStatic(MongoConnection.class);

        Mockito.when(MongoConnection.getClient()).thenReturn(mongoClient);

        // set up some expectations on the mocked MongoClient returned by MongoConnection    
        Mockito.when(mongoClient.getDatabase("aDatabaseName")).thenReturn(...);

        // ... etc
    }
} 

此类验证的对象为：

• Mockito v2.7.19
• PowerMock v1.7.0
• JUnit v4.12