Iâve sort of padded around the edges of Traits, and decided to reread the papers and better understand them. One thing that occurs to me - if you want to test your traits, is the only suggested mechanism to test them in-situ with the classes that use them OR can you poof one up and test it by explicitly pumping in something that would represent âselfâ in its usage? Or is this the wrong question - and would you view Traits as a refactoring exercise - so you write tests for a concrete class first - and then extract them into a Trait keeping the tests running? This has the thorny side effect - which like inheritance, means that ultimately you have to test a BaseClass with all its concrete subclasses (so do you have to do the same with traits? As you may have overridden something you didnât intend?). I thought maybe the paper - âReusing and Composing Tests with Traitsâ might discuss this angle, but it doesnât cover it. Any thoughts/pointers? Tim