Unit testing OCC services - Best approach

We have extended ycommerceservices to create our custom OCC services.

The newly created extension is - "mycommerceservices". The extension has "testsrc" folder under which we usually wrote unit and integration tests.

However, when using modulegen and using ycommerceservices template, another extension which is testcommerceservices is also generated. So what is the significance of this extension?

What is the best approach to wrote unit and integration tests for OCC based services?

Thanks.