Adding a test case for multivalued prompt.

Author: afoucret

x-pack/plugin/esql/qa/server/src/main/java/org/elasticsearch/xpack/esql/qa/rest/EsqlSpecTestCase.java

@@ -365,6 +365,11 @@ private Object valueMapper(CsvTestUtils.Type type, Object value) {
                 return new BigDecimal(s).round(new MathContext(7, RoundingMode.DOWN)).doubleValue();
             }
         }
+        if (type == CsvTestUtils.Type.TEXT || type == CsvTestUtils.Type.KEYWORD || type == CsvTestUtils.Type.SEMANTIC_TEXT) {
+            if (value instanceof String s) {
+                value = s.replaceAll("\\\\n", "\n");
+            }
+        }
         return value.toString();
     }
 

x-pack/plugin/esql/qa/testFixtures/src/main/resources/completion.csv-spec

@@ -14,6 +14,18 @@ Who is Victor Hugo? | WHO IS VICTOR HUGO?
 ;
 
 
+completion using a ROW source operator and prompt is a multi-valued field
+required_capability: completion
+
+ROW prompt=["Answer the following question:", "Who is Victor Hugo?"]
+| COMPLETION prompt WITH test_completion AS completion_output
+;
+
+prompt:keyword                                        | completion_output:keyword
+[Answer the following question:, Who is Victor Hugo?] | ANSWER THE FOLLOWING QUESTION:\nWHO IS VICTOR HUGO?
+;
+
+
 completion after a search
 required_capability: completion
 required_capability: match_operator_colon