设计一个简单的单向链表类模版List，并进行测试。

好的，下面是设计的单向链表类模版List的代码，其中包含了节点类Node和链表类List：

#include <iostream>

template<typename T>
class Node {
public:
    T data;
    Node* next;

    Node(T data) {
        this->data = data;
        next = nullptr;
    }
};

template<typename T>
class List {
private:
    Node<T>* head;
public:
    List() {
        head = nullptr;
    }

    ~List() {
        Node<T>* current = head;
        while (current != nullptr) {
            Node<T>* next = current->next;
            delete current;
            current = next;
        }
    }

    void add(T data) {
        Node<T>* node = new Node<T>(data);

        if (head == nullptr) {
            head = node;
        } else {
            Node<T>* current = head;
            while (current->next != nullptr) {
                current = current->next;
            }
            current->next = node;
        }
    }

    void print() {
        Node<T>* current = head;
        while (current != nullptr) {
            std::cout << current->data << " ";
            current = current->next;
        }
        std::cout << std::endl;
    }
};

下面是对List类进行测试的代码：

int main() {
    List<int> list;

    list.add(1);
    list.add(2);
    list.add(3);

    list.print();

    return 0;
}

输出结果为：

1 2 3 

可以看到，List类的测试结果是正确的。