В архиве с testlib-0.9.5 есть пример в generators/multigen.cpp:

/*
 * It is another type of generators. It writes several files named 
 * as test indices. 
 *
 * For example, this generator writes 10 files (tests) from 1 to 10.
 * This type of generators supported by Polygon too, but I believe 
 * that stdout-generators are more preferred.
 *
 * The generator for A+B problem, generates 10 tests where each 
 * number is between 1 and 100, and tests grow with indices.
 */

#include "testlib.h"
#include <iostream>

using namespace std;

void writeTest(int test)
{
    startTest(test);
    
    cout << rnd.next(1, test * test) 
        << " " << rnd.next(1, test * test) << endl;
}

int main(int argc, char* argv[])
{
    registerGen(argc, argv, 1);

    for (int i = 1; i <= 10; i++)
        writeTest(i);
    
    return 0;
}

Правда, почему-то файлы называются 1, 2, ..., 10, а не 01... или 001... .