I agree with you, however convincing an entire team of devs to explicitly separate the interface of impure parts of code is very difficult.

If you introduce a mocking library to the test portion of the codebase, most developers will start to use it as a way to shortcut any refactoring they don't want to do. I think articles like this that try to explain how to better use mocks in tests are useful, although I wish they weren't necessary.