### Question:
CoapPacket implements Serializable { public final HeaderOptions headers() { return options; } CoapPacket(InetSocketAddress remoteAddress);  CoapPacket(Code code, MessageType messageType, InetSocketAddress otherEndAddress);  CoapPacket(Method method, MessageType messageType, String uriPath, InetSocketAddress remoteAddress); static CoapPacket read(InetSocketAddress remoteAddress, byte[] rawData, int length); static CoapPacket read(InetSocketAddress remoteAddress, byte[] rawData); InetSocketAddress getRemoteAddress(); static CoapPacket deserialize(InetSocketAddress remoteAddress, InputStream inputStream); static byte[] serialize(CoapPacket coapPacket); final HeaderOptions headers(); void setHeaderOptions(HeaderOptions options); CoapPacket createResponse(); CoapPacket createResponse(Code responseCode); byte getVersion(); MessageType getMessageType(); void setMessageType(MessageType messageType); Method getMethod(); void setMethod(Method method); synchronized void setMessageId(int messageID); synchronized int getMessageId(); byte[] getPayload(); String getPayloadString(); void setPayload(String payload); void setPayload(byte[] payload); void setToken(byte[] token); byte[] getToken(); void writeTo(OutputStream outputStream); byte[] toByteArray(); Code getCode(); void setCode(Code code); boolean getMustAcknowledge(); @Override String toString(); String toString(boolean printFullPayload); String toString(boolean printFullPayload, boolean printPayloadOnlyAsHex, boolean printAddress); String toString(boolean printFullPayload, boolean printPayloadOnlyAsHex, boolean printAddress, boolean doNotPrintPayload); @Override int hashCode(); @Override boolean equals(Object obj); static final byte[] DEFAULT_TOKEN; }### Answer:
@Test public void shouldAllowObserveValueUpToThreeBytes() { CoapPacket packet = new CoapPacket(null); packet.headers().setObserve(0xFFFFFF); assertEquals(new Integer(0xFFFFFF), packet.headers().getObserve()); try { packet.headers().setObserve(0xFFFFFF + 1); fail(); } catch (IllegalArgumentException ex) { } }