Firstly if the dependency isn't doing any io, you can test your code as a whole along with its dependency. No need to mock.

More interesting is if your code relies on the outside world, then instead of abstracting out the connection with the outside world abstract out your business logic and test it separately.

So instead of a database repository being injected into your domain services, make your services rely on pure domain objects which could come from any where be it tests or the database.

Make a thin outer shell which feeds data into your domain logic from the outside world and test that via integration tests if necessary.

I'll admit I don't have the full picture here, but I have used this technique to good effect. The core idea is don't embed your infrastructure code deep inside your architecture instead move it to the very top.