Added test for render validation of PostService

[develeon]

Added basic test for render validation of PostService.

Proposing to add tests for render validation of compiletime generated services.

This will allow us to verify and better track behavior of new implementations. when using code first approach for GraphQl.

[ghostdogpr]

How about using zio-test? It's better to stick with one library.

[ghostdogpr]

Sorry I forgot about this. Could you rebase and pull the latest tags to your fork? It makes mima checks fail.