public static Instruction pushVlan() {
        return new L2ModificationInstruction.ModVlanHeaderInstruction(
                L2ModificationInstruction.L2SubType.VLAN_PUSH,
                EthType.EtherType.VLAN.ethType());
    }
@Test
    public void testPushVlanMethod() {
        final Instruction instruction = Instructions.pushVlan();
        final L2ModificationInstruction.ModVlanHeaderInstruction pushHeaderInstruction =
                checkAndConvert(instruction,
                                Instruction.Type.L2MODIFICATION,
                                L2ModificationInstruction.ModVlanHeaderInstruction.class);
        assertThat(pushHeaderInstruction.ethernetType().toString(),
                   is(EthType.EtherType.VLAN.toString()));
        assertThat(pushHeaderInstruction.subtype(),
                   is(L2ModificationInstruction.L2SubType.VLAN_PUSH));
    }