public static String padString(int level) {
        return padString(level, 2);
    }
@Test
    public void testPad() {
        assertEquals("  ", StringHelper.padString(1));
        assertEquals("    ", StringHelper.padString(2));
        assertEquals("      ", StringHelper.padString(3));
        assertEquals("   ", StringHelper.padString(3, 1));
        assertEquals(" ", StringHelper.padString(1, 1));
        assertEquals("", StringHelper.padString(0));
        assertEquals("", StringHelper.padString(0, 2));
    }