A lot of the software I write would be considered "safety critical" in that a crashed program could lead to injury to people and damage to property. Unit testi

A lot of the software I write would be considered "safety critical" in that a crashed program could lead to injury to people and damage to property. Unit testing is by far the most valuable form of testing during development, in that it catches 90% of bugs before the code touches hardware. Also, after development, unit tests serve as regression tests that catch unintended changes made by others. Mocking, whether or not through dependency injection, is absolutely necessary to enable testing when targeting bare-metal platforms, and very helpful to speed up testing when targeting an operating system. Dependency injection in particular usually constrains code to be written in a way that, although perhaps seemingly more complex at the surface, is a lot more maintainable long term. Integration testing is also a very good idea. The thing with integration tests, though, is that they get bigger and more complicated and slower over time. Relying solely on integration testing will likely become a development bottleneck if your system grows in complexity. If you can run an integration test suite deterministically and efficiently on a development system, then the software under test probably isn't that complicated, relatively speaking. Also of note is the tendency for mocks and dependency injection to help out when integration testing as well; being able to completely abstract away hardware allows for faster than real-time deterministic simulation at a system level. If you're doing well without unit tests and folk generally seem to be happy, then good on you. Unit tests are a pain to write. I'd suggest that you might be severely limiting your full potential as a software developer, though.