@Test public void isDigit() {

    for (char c = '0'; c <= '9'; c++)
        assertTrue(CharBuffer.isDigit(c));
    for (char c = 'a'; c <= 'z'; c++)
        assertFalse(CharBuffer.isDigit(c));
    for (char c = 'A'; c <= 'Z'; c++)
        assertFalse(CharBuffer.isDigit(c));
}