In functions that you write, that might be possible.

How would you assert that a given std::vector only was filtered by std::ranges::copy_if once? And how would you test that the code that was in the predicate for it wasn't duplicated?

How would you write a failing test for this function keeping the constraint that you are working with std::vector?

    std::vector<int> doThing(const std::vector<int>& nums) {
        std::vector<int> tmp1;
        std::vector<int> tmp2;
        std::ranges::copy_if(data,
                             std::back_inserter(tmp1),
                             [](int n) { return n % 2 == 0; }
        );
        std::ranges::copy_if(tmp1,
                             std::back_inserter(tmp2),
                             [](int n) { return n % 2 == 0; }
        );
        return tmp2;
    }