Once https://github.com/elastic/elasticsearch/issues/98503 is done, we can use our minimum version numbers in the SystemIndexMappingUpdate service instead of the old `Version` types. Mappings will be updated for a system index when all nodes have a matching descriptor mappings version for a system index, but this version is greater than what's stored in the mappings metadata.
server/src/test/java/org/elasticsearch/indices/SystemIndexMappingUpdateServiceTests.java
* Check that the manager will try to upgrade indices where the version in the metadata is null or absent.
     */
    public void testManagerProcessesIndicesWithNullVersionMetadata() {
        assertThat(
            SystemIndexMappingUpdateService.getUpgradeStatus(
                markShardsAvailable(createClusterState(Strings.toString(getMappings((String) null)))),
                DESCRIPTOR
            ),
            equalTo(UpgradeStatus.NEEDS_MAPPINGS_UPDATE)
        );
    }
    /**
     * Check that the manager submits the expected request for an index whose mappings are out-of-date.
     */
    public void testManagerSubmitsPutRequest() {
        SystemIndices systemIndices = new SystemIndices(List.of(FEATURE));
        SystemIndexMappingUpdateService manager = new SystemIndexMappingUpdateService(systemIndices, client);
        manager.clusterChanged(event(markShardsAvailable(createClusterState(Strings.toString(getMappings("1.0.0"))))));
        verify(client, times(1)).execute(any(PutMappingAction.class), any(PutMappingRequest.class), any());
    }
    /**
     * Check that this
     */
    public void testCanHandleIntegerMetaVersion() {
        assertThat(
            SystemIndexMappingUpdateService.getUpgradeStatus(
                markShardsAvailable(createClusterState(Strings.toString(getMappings(3)))),
                DESCRIPTOR
            ),
            equalTo(UpgradeStatus.NEEDS_MAPPINGS_UPDATE)