Comment by StephanTLavavej

Here’s what we do in MSVC’s STL:

    constexpr bool test_is_even() {
        assert(is_even(0));
        assert(!is_even(1));
        // … more test coverage
        return true;
    }
    int main() {
        test_is_even(); // runtime coverage
        static_assert(test_is_even()); // compile-time coverage

This lets us run all test cases at both runtime and compiletime. (The static_assert performs constant evaluation, and if an assert within test_is_even would fail, it won’t be a constant expression.)