Fix constand_keyword test run and properly test recent behavior change

x-pack/plugin/mapper-constant-keyword/build.gradle

@@ -1,7 +1,7 @@
 import org.elasticsearch.gradle.internal.info.BuildParams
 
 apply plugin: 'elasticsearch.internal-es-plugin'
-apply plugin: 'elasticsearch.legacy-yaml-rest-test'
+apply plugin: 'elasticsearch.internal-yaml-rest-test'
 
 esplugin {
   name 'constant-keyword'

x-pack/plugin/mapper-constant-keyword/src/main/java/org/elasticsearch/xpack/constantkeyword/ConstantKeywordFeatures.java

@@ -0,0 +1,27 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0; you may not use this file except in compliance with the Elastic License
+ * 2.0.
+ */
+
+package org.elasticsearch.xpack.constantkeyword;
+
+import org.elasticsearch.features.FeatureSpecification;
+import org.elasticsearch.features.NodeFeature;
+
+import java.util.Set;
+
+public class ConstantKeywordFeatures implements FeatureSpecification {
+    public static final NodeFeature SYNTHETIC_SOURCE_WRITE_FIX = new NodeFeature("constant_keyword.synthetic_source_write_fix");
+
+    @Override
+    public Set<NodeFeature> getFeatures() {
+        return Set.of();
+    }
+
+    @Override
+    public Set<NodeFeature> getTestFeatures() {
+        return Set.of(SYNTHETIC_SOURCE_WRITE_FIX);
+    }
+}

x-pack/plugin/mapper-constant-keyword/src/main/module-info.java

@@ -0,0 +1,18 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the "Elastic License
+ * 2.0", the "GNU Affero General Public License v3.0 only", and the "Server Side
+ * Public License v 1"; you may not use this file except in compliance with, at
+ * your election, the "Elastic License 2.0", the "GNU Affero General Public
+ * License v3.0 only", or the "Server Side Public License, v 1".
+ */
+
+module org.elasticsearch.xpack.constantkeyword {
+    requires org.elasticsearch.base;
+    requires org.elasticsearch.server;
+    requires org.elasticsearch.xcontent;
+    requires org.apache.logging.log4j;
+    requires org.apache.lucene.core;
+
+    provides org.elasticsearch.features.FeatureSpecification with org.elasticsearch.xpack.constantkeyword.ConstantKeywordFeatures;
+}

x-pack/plugin/mapper-constant-keyword/src/main/resources/META-INF/services/org.elasticsearch.features.FeatureSpecification

@@ -0,0 +1,10 @@
+#
+ # Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ # or more contributor license agreements. Licensed under the "Elastic License
+ # 2.0", the "GNU Affero General Public License v3.0 only", and the "Server Side
+ # Public License v 1"; you may not use this file except in compliance with, at
+ # your election, the "Elastic License 2.0", the "GNU Affero General Public
+ # License v3.0 only", or the "Server Side Public License, v 1".
+#
+
+org.elasticsearch.xpack.constantkeyword.ConstantKeywordFeatures

x-pack/plugin/mapper-constant-keyword/src/yamlRestTest/java/org/elasticsearch/xpack/constantkeyword/ConstantKeywordClientYamlTestSuiteIT.java

@@ -10,8 +10,10 @@
 import com.carrotsearch.randomizedtesting.annotations.Name;
 import com.carrotsearch.randomizedtesting.annotations.ParametersFactory;
 
+import org.elasticsearch.test.cluster.ElasticsearchCluster;
 import org.elasticsearch.test.rest.yaml.ClientYamlTestCandidate;
 import org.elasticsearch.test.rest.yaml.ESClientYamlSuiteTestCase;
+import org.junit.ClassRule;
 
 /** Runs yaml rest tests */
 public class ConstantKeywordClientYamlTestSuiteIT extends ESClientYamlSuiteTestCase {
@@ -24,4 +26,12 @@ public ConstantKeywordClientYamlTestSuiteIT(@Name("yaml") ClientYamlTestCandidat
     public static Iterable<Object[]> parameters() throws Exception {
         return ESClientYamlSuiteTestCase.createParameters();
     }
+
+    @ClassRule
+    public static ElasticsearchCluster cluster = ElasticsearchCluster.local().module("constant-keyword").build();
+
+    @Override
+    protected String getTestRestCluster() {
+        return cluster.getHttpAddresses();
+    }
 }

x-pack/plugin/mapper-constant-keyword/src/yamlRestTest/resources/rest-api-spec/test/20_synthetic_source.yml

@@ -1,7 +1,7 @@
 constant_keyword:
   - requires:
-      cluster_features: [ "mapper.source.mode_from_index_setting" ]
-      reason: "Source mode configured through index setting"
+      cluster_features: [ "constant_keyword.synthetic_source_write_fix" ]
+      reason: "Behavior fix"
 
   - do:
       indices.create:
@@ -26,13 +26,35 @@ constant_keyword:
         body:
           kwd: foo
 
+  - do:
+      index:
+        index:   test
+        id:      2
+        refresh: true
+        body:
+          kwd: foo
+          const_kwd: bar
+
   - do:
       search:
         index: test
         body:
           query:
             ids:
               values: [1]
+
+  - match:
+      hits.hits.0._source:
+        kwd: foo
+
+  - do:
+      search:
+        index: test
+        body:
+          query:
+            ids:
+              values: [2]
+
   - match:
       hits.hits.0._source:
         kwd: foo