protected void removeHost(MacAddress mac, VlanId vlan) {
        HostId hid = HostId.hostId(mac, vlan);
        providerService.hostVanished(hid);
    }
@Test
    public void testRemoveHost() throws Exception {
        provider.removeHost(mac, vlan);
        assertThat(providerService.hostId, is(hostId));
        assertNull(providerService.hostDescription);
        assertThat(providerService.event, is("hostVanished"));
        providerService.clear();
    }