I used to think this way, but now I believe that any method requiring writing code in a different way than the more natural one for the sake of tests is subopti

I used to think this way, but now I believe that any method requiring writing code in a different way than the more natural one for the sake of tests is suboptimal. People generally call time functions, and a good testing setup should keep your code the same (or mostly the same). Anything else makes testing less approachable, and requires extra time from developers. The provider and mocking (or a fake if you got one) approach is probably the best you can get with most programming languages.