assertEquals(expected, actual, "Base64.encode should match expected string");
    }

    /**
     * Data provider for Base64 strings and expected decoded byte arrays.
     */
    static Stream<Arguments> decodeProvider() {
        return Stream.of(Arguments.of("", new byte[0]), Arguments.of("QQ==", new byte[] { (byte) 0x41 }), // "A"
                Arguments.of("QUI=", new byte[] { (byte) 0x41, (byte) 0x42 }), // "AB"