@Override
    public Optional<Integer> partitionFor(Facility facility) {
        return Optional.ofNullable(facilityToPartitionMapping.get(facility));
    }
@Test
    public void partitionForWorksForEveryFacility() {

        FacilityPartitionMapping mapping = sampleMapping();

        for (Facility facility : Facility.values()) {
            Optional<Integer> partition = mapping.partitionFor(facility);

            assertTrue(partition.get() >= 0, "All partition numbers should be non-negative");
        }
    }