test

    std::call_once(g_once, [&] { n++; });

    CHECK(n == 1, "constinit once_flag runs once");

    CHECK(!g_shared && !g_shared_null && g_weak.expired() && !g_unique_array, "constinit pointers start empty");

    /* the destructor leaves it null: a second run is a no-op */

    alignas(std::unique_ptr<int>) unsigned char buf[sizeof(std::unique_ptr<int>)];

    auto* up = new (buf) std::unique_ptr<int>(new int(7));

    up->~unique_ptr();

    CHECK(up->get() == nullptr, "~unique_ptr leaves the pointer null");

    return 0;

}