Resolved PR comments

Author: mridula-s109

x-pack/plugin/rank-rrf/src/main/java/org/elasticsearch/xpack/rank/rrf/RRFRetrieverComponent.java

@@ -97,7 +97,13 @@ public static RRFRetrieverComponent fromXContent(XContentParser parser, Retrieve
                     parser.nextToken();
                     weight = parser.floatValue();
                 } else {
-                    throw new ParsingException(parser.getTokenLocation(), "unknown field [{}] after retriever", fieldName);
+                    throw new ParsingException(
+                        parser.getTokenLocation(),
+                        "unknown field [{}], expected [{}] or [{}]",
+                        fieldName,
+                        RETRIEVER_FIELD.getPreferredName(),
+                        WEIGHT_FIELD.getPreferredName()
+                    );
                 }
             } while (parser.nextToken() == XContentParser.Token.FIELD_NAME);
 

x-pack/plugin/rank-rrf/src/test/java/org/elasticsearch/xpack/rank/rrf/RRFRetrieverBuilderParsingTests.java

@@ -273,7 +273,7 @@ public void testRRFRetrieverComponentErrorCases() throws IOException {
             }
             """;
 
-        expectParsingException(multipleRetrieversContent, "unknown field [standard] after retriever");
+        expectParsingException(multipleRetrieversContent, "unknown field [standard], expected [retriever] or [weight]");
 
         // Test case 2: Weight without retriever
         String weightOnlyContent = """

x-pack/plugin/rank-rrf/src/yamlRestTest/resources/rest-api-spec/test/rrf/320_rrf_weighted_retriever.yml

@@ -2,7 +2,7 @@ setup:
   - requires:
       cluster_features: [ "rrf_retriever.weighted_support" ]
       reason: "RRF retriever Weighted support"
-      test_runner_features: [ "contains" ]
+      test_runner_features: [ "contains", "close_to" ]
   - do:
       indices.create:
         index: restaurants
@@ -104,6 +104,12 @@ setup:
   - match: { hits.total.value: 2 }
   - match: { hits.hits.0._id: "2" }
   - match: { hits.hits.1._id: "1" }
+  # Document 2: matches "burgers" with weight 0.9
+  # RRF score = 1/(60+1) * 0.9 = 0.01475
+  - close_to: {hits.hits.0._score: {value:  0.01475, error: 0.0001}}
+  # Document 1: matches "pizza" with weight 0.1
+  # RRF score = 1/(60+1) * 0.1 = 0.00164
+  - close_to: {hits.hits.1._score: {value:  0.00164, error: 0.0001}}
 
 ---
 "Weighted RRF retriever errors on negative weight":
@@ -130,3 +136,4 @@ setup:
                   weight: 0.7
   - match: { error.type: "x_content_parse_exception" }
   - contains: { error.reason: "failed to parse field" }
+