Score 0 test case added to check for corner cases

Author: mridula-s109

x-pack/plugin/rank-rrf/src/yamlRestTest/resources/rest-api-spec/test/linear/10_linear_retriever.yml

@@ -318,6 +318,40 @@ setup:
   - match: { hits.hits.3._id: "3" }
   - match: { hits.hits.3._score: 1.2 }
 
+---
+"should handle all zero scores in normalization":
+  - do:
+      search:
+        index: test
+        body:
+          retriever:
+            linear:
+              retrievers: [
+                {
+                  retriever: {
+                    standard: {
+                      query: {
+                        bool: {
+                          should: [
+                            { constant_score: { filter: { term: { keyword: { value: "one" } } }, boost: 0.0 } },
+                            { constant_score: { filter: { term: { keyword: { value: "two" } } }, boost: 0.0 } },
+                            { constant_score: { filter: { term: { keyword: { value: "three" } } }, boost: 0.0 } },
+                            { constant_score: { filter: { term: { keyword: { value: "four" } } }, boost: 0.0 } }
+                          ]
+                        }
+                      }
+                    }
+                  },
+                  weight: 1.0,
+                  normalizer: "l2_norm"
+                }
+              ]
+  - match: { hits.total.value: 4 }
+  - close_to: { hits.hits.0._score: { value: 0.0, error: 0.0001 } }
+  - close_to: { hits.hits.1._score: { value: 0.0, error: 0.0001 } }
+  - close_to: { hits.hits.2._score: { value: 0.0, error: 0.0001 } }
+  - close_to: { hits.hits.3._score: { value: 0.0, error: 0.0001 } }
+
 ---
 "should throw on unknown normalizer":
   - do: