public static L2ModificationInstruction modVlanId(VlanId vlanId) {
        checkNotNull(vlanId, "VLAN id cannot be null");
        return new L2ModificationInstruction.ModVlanIdInstruction(vlanId);
    }
@Test
    public void testModVlanIdMethod() {
        final Instruction instruction = Instructions.modVlanId(vlanId1);
        final L2ModificationInstruction.ModVlanIdInstruction modEtherInstruction =
                checkAndConvert(instruction,
                        Instruction.Type.L2MODIFICATION,
                        L2ModificationInstruction.ModVlanIdInstruction.class);
        assertThat(modEtherInstruction.vlanId(), is(equalTo(vlanId1)));
        assertThat(modEtherInstruction.subtype(),
                is(equalTo(L2ModificationInstruction.L2SubType.VLAN_ID)));
    }