Should I use assert to verify a third party function?

I use some third party function which based on the filter returns specified number of objects:

//void GetObjects(std::vector<T>&, Filter, int /*objectsNumber*/)

GetObjects(vec, filter, 1);

if(vec.empty())
{
   throw ObjectNotFound();
}

assert(vec.size() == 1);

Should I use assert like above ? Is it a typical assert scenario ?