csv test for reusing column names

Author: jan-elastic

x-pack/plugin/esql/compute/src/main/java/org/elasticsearch/compute/operator/ChangePointOperator.java

@@ -66,8 +66,10 @@ public void addInput(Page page) {
 
     @Override
     public void finish() {
-        finished = true;
-        createOutputPages();
+        if (finished == false) {
+            finished = true;
+            createOutputPages();
+        }
     }
 
     @Override
@@ -135,7 +137,6 @@ private void createOutputPages() {
                 changePvalueBlock = blockFactory.newConstantNullBlock(inputPage.getPositionCount());
             }
 
-            // TODO: what about duplicate names??
             Page outputPage = inputPage.appendBlocks(new Block[] { changeTypeBlock, changePvalueBlock });
             outputPages.add(outputPage);
             pageStartIndex += inputPage.getPositionCount();

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

@@ -170,3 +170,39 @@ height:double | salary:double      | type:text | pvalue:double
 2.09          | 38645.0            | null      | null                
 2.1           | 0.0                | dip       | 9.590143836835097E-6  
 ;
+
+
+reuse column names
+// TODO: required_capability: change_point
+
+FROM k8s
+  | STATS count=COUNT() BY @timestamp=BUCKET(@timestamp, 1 MINUTE)
+  | EVAL count=count+CASE(@timestamp=="2024-05-10T00:08:00.000Z", 100, 0)
+  | CHANGE_POINT count ON @timestamp AS @timestamp, count
+;
+
+@timestamp:text | count:double
+null            | null
+null            | null
+null            | null
+null            | null
+null            | null
+null            | null
+null            | null
+null            | null
+spike           | 1.7502597878858522E-193
+null            | null
+null            | null
+null            | null
+null            | null
+null            | null
+null            | null
+null            | null
+null            | null
+null            | null
+null            | null
+null            | null
+null            | null
+null            | null
+null            | null
+;