> But, how do you systematically unit test nested functions? Why, with nested unittests, of course! Just put them in a nested type first: void main() {

> But, how do you systematically unit test nested functions? Why, with nested unittests, of course! Just put them in a nested type first: void main() { static int nested(int x) { return x * 2; } struct Test { unittest { assert(nested(2) == 4); } } } Well, OK, that's more of a hack than a feature, and you obviously can't test non-static nested functions (as there'd be no way to give values to the outer function's frame variables). But you asked :)