Fix BwC synonyms tests (#118691)

Author: carlosdelest

muted-tests.yml

@@ -156,9 +156,6 @@ tests:
   issue: https://github.com/elastic/elasticsearch/issues/117473
 - class: org.elasticsearch.repositories.s3.RepositoryS3EcsClientYamlTestSuiteIT
   issue: https://github.com/elastic/elasticsearch/issues/117525
-- class: org.elasticsearch.backwards.MixedClusterClientYamlTestSuiteIT
-  method: test {p0=synonyms/90_synonyms_reloading_for_synset/Reload analyzers for specific synonym set}
-  issue: https://github.com/elastic/elasticsearch/issues/116777
 - class: "org.elasticsearch.xpack.esql.qa.multi_node.EsqlSpecIT"
   method: "test {scoring.*}"
   issue: https://github.com/elastic/elasticsearch/issues/117641

rest-api-spec/build.gradle

@@ -69,4 +69,5 @@ tasks.named("yamlRestCompatTestTransform").configure ({ task ->
   task.skipTest("search/520_fetch_fields/fetch _seq_no via fields", "error code is changed from 5xx to 400 in 9.0")
   task.skipTest("search.vectors/41_knn_search_bbq_hnsw/Test knn search", "Scoring has changed in latest versions")
   task.skipTest("search.vectors/42_knn_search_bbq_flat/Test knn search", "Scoring has changed in latest versions")
+  task.skipTest("synonyms/90_synonyms_reloading_for_synset/Reload analyzers for specific synonym set", "Can't work until auto-expand replicas is 0-1 for synonyms index")
 })

rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/synonyms/90_synonyms_reloading_for_synset.yml

@@ -1,8 +1,8 @@
----
-"Reload analyzers for specific synonym set":
+setup:
   - requires:
       cluster_features: ["gte_v8.10.0"]
       reason: Reloading analyzers for specific synonym set is introduced in 8.10.0
+
   # Create synonyms_set1
   - do:
       synonyms.put_synonym:
@@ -100,21 +100,25 @@
           - '{"index": {"_index": "my_index2", "_id": "2"}}'
           - '{"my_field": "goodbye"}'
 
-  # An update of synonyms_set1 must trigger auto-reloading of analyzers only for synonyms_set1
+---
+"Reload analyzers for specific synonym set":
+# These specific tests can't succeed in BwC, as synonyms auto-expand replicas are 0-all. Replicas can't be associated to
+#  upgraded nodes, and thus we are not able to guarantee that the shards are not failed.
+# This test is skipped for BwC until synonyms index has auto-exapnd replicas set to 0-1.
+
   - do:
       synonyms.put_synonym:
         id: synonyms_set1
         body:
           synonyms_set:
             - synonyms: "hello, salute"
             - synonyms: "ciao => goodbye"
+
   - match: { result: "updated" }
   - gt: { reload_analyzers_details._shards.total: 0 }
   - gt: { reload_analyzers_details._shards.successful: 0 }
   - match: { reload_analyzers_details._shards.failed: 0 }
-  - length: { reload_analyzers_details.reload_details: 1 } # reload details contain only a single index
-  - match: { reload_analyzers_details.reload_details.0.index: "my_index1" }
-  - match: { reload_analyzers_details.reload_details.0.reloaded_analyzers.0: "my_analyzer1" }
+
 
   # Confirm that the index analyzers are reloaded for my_index1
   - do:
@@ -127,6 +131,23 @@
                 query: salute
   - match: { hits.total.value: 1 }
 
+---
+"Check analyzer reloaded and non failed shards for bwc tests":
+
+  - do:
+      synonyms.put_synonym:
+        id: synonyms_set1
+        body:
+          synonyms_set:
+            - synonyms: "hello, salute"
+            - synonyms: "ciao => goodbye"
+  - match: { result: "updated" }
+  - gt: { reload_analyzers_details._shards.total: 0 }
+  - gt: { reload_analyzers_details._shards.successful: 0 }
+  - length: { reload_analyzers_details.reload_details: 1 } # reload details contain only a single index
+  - match: { reload_analyzers_details.reload_details.0.index: "my_index1" }
+  - match: { reload_analyzers_details.reload_details.0.reloaded_analyzers.0: "my_analyzer1" }
+
   # Confirm that the index analyzers are still the same for my_index2
   - do:
       search: