assertNotNull(result);
        assertEquals(16, result.length);

        // Calculate the same using manual HMACT64 algorithm
        byte[] expectedResult = calculateHMACT64Manually(key, data);
        assertArrayEquals(expectedResult, result);
    }

    @Test
    void testHMACT64WithEmptyData() {
        // Test with empty data
        HMACT64 hmac = new HMACT64(TEST_KEY);