byte[] result = hmac.engineDigest();

        assertNotNull(result);
        assertEquals(16, result.length); // MD5 produces 16 bytes
    }

    @Test
    void testEngineDigestWithBuffer() {
        // Test engineDigest(byte[] buf, int offset, int len)
        HMACT64 hmac = new HMACT64(TEST_KEY);
        hmac.engineUpdate(TEST_DATA, 0, TEST_DATA.length);

        byte[] buffer = new byte[32];

            verify(mockMd5, times(1)).digest(innerDigest); // Second call for final digest
        }
    }

    @Test
    void testEngineDigestWithBuffer() throws NoSuchAlgorithmException, DigestException {
        // Test engineDigest(byte[] buf, int offset, int len)
        try (MockedStatic<Crypto> mockedCrypto = mockStatic(Crypto.class)) {