Hi Dave,
If you're just checking MPL assertions, then presumably there's a predicate that can be evaluated without throwing. Why not just feed those predicates' results to regular runtime assertions?
In addition to feeding those predicates to runtime assertions a type pretty-printing utility can be used to provide more detail on why the predicate failed. Relying on a pretty-printer rather than the compiler error messages makes the output standard across platforms/compilers and more readable in many cases. For example for the following predicate: typedef equal_to<int_<13>, function_to_test<int_<7> >::type> p; it can provide a reason like "equal_to<int_<13>, int_<11> >" compared to a verbose compiler error message containing the point somewhere. The difference becomes more significant when there are more failed predicates and a unit testing report can list and clearly separate the failed test cases (and their reasons) from each other. I found this very useful while I was developing metaprogramming libraries. This thing can be wrapped by something (template function, macro, etc) taking the predicate as a nullary metafunction. That wrapper can either give the result of the predicate and the pretty-printed reason to a runtime assertion or collect them somewhere. In the latter case, an integration tool can feed them to runtime assertions which makes template metaprogramming tests independent of the tool being used to test runtime code. Regards, Abel