Minor fix and added some docs

Author: ivancea

x-pack/plugin/esql/compute/src/test/java/org/elasticsearch/compute/aggregation/GroupingAggregatorFunctionTestCase.java

@@ -781,6 +781,14 @@ public String describe() {
         };
     }
 
+    /**
+     * Custom {@link HashAggregationOperator.HashAggregationOperatorFactory} implementation that
+     * randomizes the GroupIds block type passed to AddInput.
+     * <p>
+     *     This helps testing the different overloads of
+     *     {@link org.elasticsearch.compute.aggregation.GroupingAggregatorFunction.AddInput#add}
+     * </p>
+     */
     private record RandomizingHashAggregationOperatorFactory(
         List<BlockHash.GroupSpec> groups,
         AggregatorMode aggregatorMode,

x-pack/plugin/esql/compute/src/test/java/org/elasticsearch/compute/data/BlockTypeRandomizer.java

@@ -72,7 +72,7 @@ public static IntBlock randomizeBlockType(IntBlock block) {
         // IntArrayBlock
         //
         if (randomIntBetween(0, --classCount) == 0) {
-            if (block instanceof IntVectorBlock) {
+            if (block instanceof IntArrayBlock) {
                 return block;
             }