public static Instruction popVlan() {
        return new L2ModificationInstruction.ModVlanHeaderInstruction(
                L2ModificationInstruction.L2SubType.VLAN_POP);
    }
@Test
    public void testPopVlanMethod() {
        final Instruction instruction = Instructions.popVlan();
        final L2ModificationInstruction.ModVlanHeaderInstruction popVlanInstruction =
                checkAndConvert(instruction,
                                Instruction.Type.L2MODIFICATION,
                                L2ModificationInstruction.ModVlanHeaderInstruction.class);
        assertThat(popVlanInstruction.subtype(),
                   is(L2ModificationInstruction.L2SubType.VLAN_POP));
    }