What is the best practice for [Testing] in no-live env without live env resources?

Let me explain this question in detail.

Background

Normally, we develop service/feature/system in no-live network and test the code also in no-live network. However, sometimes there are some dependencies which need to be accessed through live network. But it's not good to test the code in the live network directly since it may affect the online services.

Question

What is the best practice to solve such headache? (If some dependencies only can be accessed from live env)

Notes

in live network, we may have liveish env and live env