assertEquals(0, c1.compareTo(c2), "expected " + v1 + " == " + v2);
        assertEquals(0, c2.compareTo(c1), "expected " + v2 + " == " + v1);
    }

    private void checkVersionsArrayEqual(String[] array) {
        // compare against each other (including itself)
        for (int i = 0; i < array.length; ++i)
            for (int j = i; j < array.length; ++j) checkVersionsEqual(array[i], array[j]);