@Test
void isEmpty() {

    assertThat(RoutingPlan.empty().isEmpty()).isTrue();
    assertThat(new RoutingPlan(Distance.ZERO, emptyList(), depot, emptyList(), emptyList()).isEmpty()).isFalse();
    assertThat(new RoutingPlan(Distance.ZERO, vehicles, null, emptyList(), emptyList()).isEmpty()).isFalse();
    assertThat(new RoutingPlan(Distance.ZERO, vehicles, depot, emptyList(), singletonList(emptyRoute)).isEmpty())
            .isFalse();
}