### Question:
ServerParser { public static void decodePayload(Object data, Parser.DecodePayloadCallback callback) { assert callback != null; ArrayList<Packet> packets = new ArrayList<>(); if(data instanceof String) { final String stringData = (String) data; for (int payloadIdx = 0; payloadIdx < stringData.length(); ) { final int separatorIdx = stringData.indexOf(':', payloadIdx); if(separatorIdx < 0) { throw new IllegalArgumentException("Invalid payload: " + stringData); } int length = Integer.parseInt(stringData.substring(payloadIdx, separatorIdx)); String packetData = stringData.substring( separatorIdx + 1, length + separatorIdx + 1); Packet packet = decodePacket(packetData); packets.add(packet); payloadIdx = length + separatorIdx + 1; } } else if(data instanceof byte[]) { final byte[] byteData = (byte[]) data; for (int payloadIdx = 0; payloadIdx < byteData.length; ) { final boolean isBinary = (byteData[payloadIdx] == 1); final int lengthStartIdx = payloadIdx + 1; int lengthEndIdx = lengthStartIdx; while (byteData[lengthEndIdx] != -1) { lengthEndIdx++; } StringBuilder lengthString = new StringBuilder(); for (int l = lengthStartIdx; l < lengthEndIdx; l++) { char digit = (char) ('0' + byteData[l]); lengthString.append(digit); } final int length = Integer.parseInt(lengthString.toString()); byte[] bufferData = new byte[length]; System.arraycopy(byteData, lengthEndIdx + 1, bufferData, 0, bufferData.length); Packet packet; if(isBinary) { packet = decodePacket(bufferData); } else { packet = decodePacket(new String(bufferData, StandardCharsets.UTF_8)); } packets.add(packet); payloadIdx = lengthEndIdx + length + 1; } } for (int i = 0; i < packets.size(); i++) { if(!callback.call(packets.get(i), i, packets.size())) { return; } } } private  ServerParser(); static void encodePacket(Packet packet, boolean supportsBinary, Parser.EncodeCallback callback); static void encodePayload(List<Packet<?>> packets, boolean supportsBinary, Parser.EncodeCallback callback); @SuppressWarnings("Duplicates") static void encodePayloadAsBinary(List<Packet<?>> packets, Parser.EncodeCallback<byte[]> callback); static Packet decodePacket(Object data); static void decodePayload(Object data, Parser.DecodePayloadCallback callback); @SuppressWarnings("WeakerAccess")
    static final int PROTOCOL; }### Answer:
@Test(expected = IllegalArgumentException.class) public void testDecodePayload_error() { ServerParser.decodePayload("abcxyz", (packet, index, total) -> false); }