Testing userRouter and userService

[viktor-c]

Hi Edwin! Thank you for sharing this great project! I really liked it and learned some new things along.
I setup mongoose and mongodb as bakend.
When testing userRouter.test.ts I initialize the database connection, tests pass.
However when testing userService.test.ts I get an error because the database does not get initialized through the backend.
Why do I need to test the service, it should already work as expected if it connected to the database and passed the router tests?
Am I missing something?