Fix a mappings update test (#33146)

This commit fixes a mappings update test. The test is broken in the
sense that it passes, but for the wrong reason. The test here is testing
that if we make a mapping update but do not commit that mapping update
then the mapper service still maintains the previous document
mapper. This was not the case long, long ago when a mapping update would
update the in-memory state before the cluster state update was
committed. This test was passing, but it was passing because the mapping
update was never even updated. It was never even updated because it was
encountering a null pointer exception. Of course the in-memory state is
not going to be updated in that case, we are simply going to end up with
a failed cluster state update. Fixing that leads to another issue which
is that the mapping source does not even parse so again we would, of
course, end up with the in-memory state not being modified. We fix these
issues, assert that the result cluster state task completed
successfully, and finally that the in-memory state was not updated since
we never committed the resulting cluster state.

server/src/test/java/org/elasticsearch/cluster/metadata/MetaDataMappingServiceTests.java

@@ -16,12 +16,15 @@
  * specific language governing permissions and limitations
  * under the License.
  */
+
 package org.elasticsearch.cluster.metadata;
 
 import org.elasticsearch.action.admin.indices.mapping.put.PutMappingClusterStateUpdateRequest;
 import org.elasticsearch.cluster.ClusterState;
+import org.elasticsearch.cluster.ClusterStateTaskExecutor;
 import org.elasticsearch.cluster.service.ClusterService;
 import org.elasticsearch.common.compress.CompressedXContent;
+import org.elasticsearch.index.Index;
 import org.elasticsearch.index.IndexService;
 import org.elasticsearch.plugins.Plugin;
 import org.elasticsearch.test.ESSingleNodeTestCase;
@@ -31,6 +34,7 @@ import java.util.Collection;
 import java.util.Collections;
 
 import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.not;
 
 public class MetaDataMappingServiceTests extends ESSingleNodeTestCase {
 
@@ -47,8 +51,18 @@ public class MetaDataMappingServiceTests extends ESSingleNodeTestCase {
         final ClusterService clusterService = getInstanceFromNode(ClusterService.class);
         // TODO - it will be nice to get a random mapping generator
         final PutMappingClusterStateUpdateRequest request = new PutMappingClusterStateUpdateRequest().type("type");
-        request.source("{ \"properties\" { \"field\": { \"type\": \"text\" }}}");
-        mappingService.putMappingExecutor.execute(clusterService.state(), Collections.singletonList(request));
+        request.indices(new Index[] {indexService.index()});
+        request.source("{ \"properties\": { \"field\": { \"type\": \"text\" }}}");
+        final ClusterStateTaskExecutor.ClusterTasksResult<PutMappingClusterStateUpdateRequest> result =
+                mappingService.putMappingExecutor.execute(clusterService.state(), Collections.singletonList(request));
+        // the task completed successfully
+        assertThat(result.executionResults.size(), equalTo(1));
+        assertTrue(result.executionResults.values().iterator().next().isSuccess());
+        // the task really was a mapping update
+        assertThat(
+                indexService.mapperService().documentMapper("type").mappingSource(),
+                not(equalTo(result.resultingState.metaData().index("test").mapping("type").source())));
+        // since we never committed the cluster state update, the in-memory state is unchanged
         assertThat(indexService.mapperService().documentMapper("type").mappingSource(), equalTo(currentMapping));
     }
 
@@ -69,4 +83,5 @@ public class MetaDataMappingServiceTests extends ESSingleNodeTestCase {
 
         assertSame(result, result2);
     }
+
 }