it may been born in the smalltalk world, but it really was worked fleshed out and challenged and hashed and rehashed in the world of java ( and mirrored in other languages like C++, C#, and ruby ). The XP forum was very active in building what it meant to unit test and how to do test first development, it was highly motivated by the idea of being able to robustly respond to change with quick feedback loops. What became apparent is that the smalltalk world of small modular highly composable designs is kind of critical and much of the C++ / Java world struggled to achieve that, but there was a lot of advice on design techniques. Over time what's been left is more of an emphasis on test than design when talking about that pros and cons of unit testing. So we now want to validate our software works more than we want techniques to quickly evolve our designs and adapt to change in a robust way. Both achieve the idea of working software. So unit testing as a technique to test your software works may not be as good as integration testing and E2E testing, but that wasn't its sole goal, adaptable design was. Not that design has been left behind, if anything we are seeing quite a lot of focus on things like functional programming and new design ideas for putting software together. The key thing is not really the dogma of practices but the ideas of working software and adapting to change and that the idea of robustness and good design is embraced in the core of what you do.