eg
```
"impacts": [
            {
              "severity": 3,
              "description": "Searches might return slower than usual. Fewer redundant copies of the data exist on 2 indices [.ds-logslogslogs-2022.03.29-000001, my-index-000001].",
              "impact_areas": [ "search" ]
            }
          ]
```
server/src/test/java/org/elasticsearch/cluster/routing/allocation/ShardsAvailabilityHealthIndicatorServiceTests.java
);
    }
    public void testSortByIndexPriority() {
        var lowPriority = randomIntBetween(1, 5);
        var highPriority = randomIntBetween(6, 20);
        List<IndexMetadata> indexMetadataList = createIndexMetadataForIndexNameToPriorityMap(
            Map.of("index-3", lowPriority, "index-1", lowPriority, "index-2", highPriority)
        );
        var clusterState = createClusterStateWith(
            List.of(
                index("index-3", new ShardAllocation(randomNodeId(), AVAILABLE), new ShardAllocation(randomNodeId(), UNAVAILABLE)),
                index("index-1", new ShardAllocation(randomNodeId(), AVAILABLE), new ShardAllocation(randomNodeId(), UNAVAILABLE)),
                index("index-2", new ShardAllocation(randomNodeId(), AVAILABLE), new ShardAllocation(randomNodeId(), UNAVAILABLE))
            ),
            List.of(),
            indexMetadataList
        );
        var service = createAllocationHealthIndicatorService(clusterState);
        HealthIndicatorResult result = service.calculate(true);
        
        assertThat(
            result.impacts().get(0),
            equalTo(
                new HealthIndicatorImpact(
                    3,
                    "Searches might return slower than usual. Fewer redundant copies of the data exist on 3 indices [index-2, "
                        + "index-1, index-3]."
                )
            )
        );