@Test
public void testFromHexStringError() {

    String invalidStr = "00:00:00:00:00:00:ffff";
    try {
        HexString.fromHexString(invalidStr);
        fail("HexString.fromHexString() should have thrown a NumberFormatException");
    }
    catch (NumberFormatException expected) {
        // do nothing
    }
}