Error when using PROGMEM strings and DEBUG with PSTR() in template functions

test.h

#ifndef TEST_H
#define TEST_H


#define TEST Serial

const char testString[] PROGMEM = "Test String"; 


#if defined(TEST)
#define DEBUG(_1, ...) { TEST.printf_P( PSTR(_1) ,##__VA_ARGS__); }
#else
#define DEBUG(...) {}
#endif

template<typename T>
class testClass {
public:
  void a(); 
  
};


#include "test.hpp"

#endif

test.hpp

template<typename T> 
void testClass<T>::a() {
  DEBUG("abc");
  Serial.println(FPSTR(testString)); 
}

testsketch.ino

#include "test.h"


testClass<int> a; 


void setup() {
  // put your setup code here, to run once:
  a.a();

}

void loop() {
  // put your main code here, to run repeatedly:

}