Mechanisms of community assembly are increasingly explored by combining community and species trait data with null models. By investigating if the traits of co-existing species are more similar (trait convergence) or more dissimilar (trait divergence) than expected by chance, these tests relate observed patterns to different co-existence mechanisms. Do null models accurately detect trait convergence and divergence? Are different null models equally good at detecting these two opposing patterns? How important are the species pool and other constraints that are considered by different null models?