how to refer dubbo service in unit test

- [x] I have searched the [issues](https://github.com/apache/dubbo/issues) of this repository and believe that this is not a duplicate.
- [x] I have checked the [FAQ](https://github.com/apache/dubbo/blob/master/FAQ.md) of this repository and believe that this is not a duplicate.

### Environment

* Dubbo version: 2.7.10
* Operating System version: MacOs 10.14.2
* Java version: 1.8.0_151

### Steps to reproduce this issue

1. define a dubbo service and export to nacos
2. in unit test(will start SpringBoot) refer this service and config injvm = false
3. the service cannot be found

Pls. provide [GitHub address] to reproduce this issue.

### Expected Result

refer dubbo service can be invoked

### Actual Result

dubbo service provider can't be found