public static L4ModificationInstruction modUdpDst(TpPort port) {
        checkNotNull(port, "Dst UDP port cannot be null");
        return new ModTransportPortInstruction(L4SubType.UDP_DST, port);
    }
@Test
    public void testModUdpDstMethod() {
        final Instruction instruction = Instructions.modUdpDst(tpPort1);
        final L4ModificationInstruction.ModTransportPortInstruction modTransportPortInstruction =
                checkAndConvert(instruction, Instruction.Type.L4MODIFICATION,
                                L4ModificationInstruction.ModTransportPortInstruction.class);
        assertThat(modTransportPortInstruction.port(), is(equalTo(tpPort1)));
        assertThat(modTransportPortInstruction.subtype(),
                   is(equalTo(L4ModificationInstruction.L4SubType.UDP_DST)));
    }