public static L3ModificationInstruction modArpSpa(IpAddress addr) {
        checkNotNull(addr, "Src l3 ARP IP address cannot be null");
        return new ModArpIPInstruction(L3SubType.ARP_SPA, addr);
    }
@Test
    public void testModArpSpaMethod() {
        final Instruction instruction = Instructions.modArpSpa(ip41);
        final L3ModificationInstruction.ModArpIPInstruction modArpIPInstruction =
                checkAndConvert(instruction,
                                Instruction.Type.L3MODIFICATION,
                                L3ModificationInstruction.ModArpIPInstruction.class);
        assertThat(modArpIPInstruction.subtype(),
                   is(L3ModificationInstruction.L3SubType.ARP_SPA));
        assertThat(modArpIPInstruction.ip(), is(ip41));
    }