@Test
    public void next_2Threads10Numbers_NoDuplicatesAndMissingVal() {
        ExecutorService es = Executors.newFixedThreadPool(2);
        ConcGeomProgression cgp = new ConcGeomProgression();
        
        GeomProber.setCounter(10);
        
        for (int i = 0; i < 2; ++i) {
            es.submit(new GeomProber(cgp));
        }
        
        es.shutdown();
        
        for (int i = 1; i <= results.size(); ++i) {

            // check no values were skipped
            assertTrue("Value " + i + " is missing",
                    results.containsKey(new BigInteger(Integer.toString(i))));
        }
    }