@Test
public void Should_enumerate_returnListOfIdentifiersOfAllReceivers()
        throws Exception {

    Set<Object> keys = new HashSet<>(Arrays.asList(new Object(), new Object()));
    Map<Object, IMessageReceiver> mapMock = mock(Map.class);
    when(mapMock.keySet()).thenReturn(keys);
    IRouter router = new MapRouter(mapMock);
    assertEquals(new ArrayList<Object>(keys), router.enumerate());
}