mapping a pair to a struct

There are no overload of std::map::insert that takes a key and a value.

You can use operator[] to add a new element:

   mp[key] = *obj;

Or std::map::insert_or_assign since C++17:

   mp.insert_or_assign(key, *obj);

Another point is that type of obj is test* while the type of values of the map mp has type test. The pointer should be dereferenced (like my examples above) or the type of values should be changed to pointers to do this insertion.