以下程序将打印什么字符串输出?

#define MESG this is a test 

#include <stdio.h> 

int main(void) { 
   int n = 0; 

   while ( n < 5 ) 
      printf(%s\n, MESG); 
      n++; 
   printf(That's all.\n); 
   return 0; 
}