[j_kao]

Testing in production will trend upwards among companies because everybody's workload is shifting towards the cloud and/or making use of external SaaS services. There are a number of cloud services that are not open source that can't be run locally, or run at the same scale as production.

It is not a good use of time to mock everything, because you have no control of external systems. The only reason I'd see it being important is if these external systems are tightly coupled to complex local logic that should be tested locally. However, there are a number of strategies to deal with such "tight coupling" in such cases.