During the development and review process of the disk health indicator we noticed that it was hard to understand. Since we learnt a lot from the first round of development we want to go through the code one more time and restructure it.
server/src/test/java/org/elasticsearch/health/node/DiskHealthIndicatorServiceTests.java
HealthStatus.RED,
            numberOfRedNonDataNonMasterNodes,
            nonDataNonMasterDiscoveryNodes,
            HealthStatus.YELLOW,
            numberOfYellowDataNodes,
            dataDiscoveryNodes
        );
        HealthIndicatorResult result = diskHealthIndicatorService.calculate(true, healthInfo);
        assertThat(result.status(), equalTo(HealthStatus.RED));
        assertThat(
            result.symptom(),
            equalTo(
                "1 index is not allowed to be updated because "
                    + (numberOfYellowDataNodes + (numberOfYellowDataNodes == 1 ? " node is" : " nodes are"))
                    + " out of disk or running low on disk space. Furthermore "
                    + (numberOfRedMasterNodes + numberOfRedNonDataNonMasterNodes)
                    + " nodes with roles: "
                    + Stream.concat(masterRole.stream(), nonDataNonMasterRoles.stream()).map(DiscoveryNodeRole::roleName).sorted().toList()
                    + " are out of disk or running low on disk space."
            )
        );
        List<HealthIndicatorImpact> impacts = result.impacts();
        assertThat(impacts.size(), equalTo(3));
        assertThat(impacts.get(0).impactDescription(), containsString("Cannot insert or update documents in the affected indices ["));
        assertThat(impacts.get(0).severity(), equalTo(1));
        assertThat(impacts.get(0).impactAreas(), equalTo(List.of(ImpactArea.INGEST)));
        assertThat(impacts.get(1).impactDescription(), equalTo("Cluster stability might be impaired."));
        assertThat(impacts.get(1).severity(), equalTo(2));
        assertThat(impacts.get(1).impactAreas(), equalTo(List.of(ImpactArea.DEPLOYMENT_MANAGEMENT)));
        assertThat(