How to write test for C++ templates?

Question

Suppose I am writing a template library consisting of a function template

template<T> void f(T);

with the requirement that it works with a predefined set of classes A, B, C, and D, e.g., the following must compile:

template<> void f(A);
template<> void f(B);
template<> void f(C);
template<> void f(D);

Which test framework can I use to write test cases that captures this requirement at runtime instead of failing at compilation of the test code? In another word, I would like the framework to instantiate the templates at runtime and produce a nicely formatted error report if a subset of them fails.

I know I can forego test frameworks altogether and simply write a simple cc file containing the 4 lines above. But I was hoping I could incorporate this requirement into regular, standard test cases for generation of test status reports. For example,

test f works with A: passed.
test f works with B: passed.
test f works with C: failed!  Cannot cast type C!
test f works with D: passed.

3 of 4 tests passed.
1 of 4 tests failed.

Answer 1

Write a test case that spawns the compiler... that's how e.g. autoconf tests for existence of features.

Answer 2

I don't understand why failing at runtime is preferable to failing at compile time. The earlier you fail in the unit testing process the better. It is preferable to have your unit tests not compile than fail. Its even easier to fix, In fact it probably won't even be committed to source control. Your unit test should just include those four lines and assert true at the end. Note this isn't the way I would go about doing it myself.