c++ - I have three cpp file.I want test that template class declaration and definition in different file.but i got failed

this is my code snnippet

// test.cpp
#include 
#include "test.h"
int main(){
  Test test = Test();

  test.add(1);
  test.print();
}


// test.h
#ifndef TEST
#define TEST
template  class Test{
public:
  T info;
  void print();
  void add(T i);
 };
#endif

// testT.cpp
#include 
#include "test.h"

template void Test::print()
{
   std::cout << info << std::endl;
}
template void Test::add(T i)
{

  info = i;
}

and i run this exec

g++ -c testT.cpp && g++ test.cpp -o a.out testT.o

i get this error

Undefined symbols for architecture x86_64:
  "Test::add(int)", referenced from:
      _main in test-e89092.o
  "Test::print()", referenced from:
      _main in test-e89092.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)  // in my macOS

i want to declare template class in head file and define method in other file,so i only compile the define method file not head file if i change the definition of method in template class. what should i do?