We care about writing quality code, we have read the definition of SOLID principles several times and we know how important they are for writing good OO code, but are we really following those principles? Is there a pragmatic way of following them in our day to day jobs or are they just some principles a few computer scientists wrote? Fortunately there is, SOLID principles are not just good ideas , they are intended to help us write better code, enjoy our jobs more and be happy programmers. But, where should we start? We should start where we always do. By writing tests, yes, for real. As Kent Beck says "TDD doesn't drive good design. TDD gives you immediate feedback about what is likely to be bad design", so we need to go a step further. In this talk we will see how writing tests is not just *doing TDD* is about having good test coverage, it's also about driving our code towards good design, one that follows SOLID principles.