Updated tests to fit new query hierarchy

Author: sawansri

CHANGELOG.md

@@ -52,6 +52,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Approximation Framework Enhancement: Update the BKD traversal logic to improve the performance on skewed data ([#18439](https://github.com/opensearch-project/OpenSearch/issues/18439))
 - Support system generated ingest pipelines for bulk update operations ([#18277](https://github.com/opensearch-project/OpenSearch/pull/18277)))
 - Added FS Health Check Failure metric ([#18435](https://github.com/opensearch-project/OpenSearch/pull/18435))
+- Added approximation support for range queries with now in date field ([#18511](https://github.com/opensearch-project/OpenSearch/pull/18511))
 
 ### Changed
 - Create generic DocRequest to better categorize ActionRequests ([#18269](https://github.com/opensearch-project/OpenSearch/pull/18269)))

server/src/main/java/org/opensearch/index/mapper/DateFieldMapper.java

@@ -602,7 +602,6 @@ public static Query handleNow(QueryShardContext context, Function<LongSupplier,
             }
 
             return query;
-//            return nowUsed[0] ? new DateRangeIncludingNowQuery(query) : query;
         }
 
         public long parseToLong(Object value, boolean roundUp, @Nullable ZoneId zone, DateMathParser dateParser, LongSupplier now) {

server/src/test/java/org/opensearch/index/query/RangeQueryBuilderTests.java

@@ -440,14 +440,23 @@ public void testDateRangeQueryTimezone() throws IOException {
             + "        }\n"
             + "    }\n"
             + "}";
+
+        // TODO what else can we assert
         QueryShardContext context = createShardContext();
         Query parsedQuery = parseQuery(query).toQuery(context);
-        assertThat(parsedQuery, instanceOf(DateRangeIncludingNowQuery.class));
-        parsedQuery = ((DateRangeIncludingNowQuery) parsedQuery).getQuery();
+
         assertThat(parsedQuery, instanceOf(ApproximateScoreQuery.class));
-        parsedQuery = ((ApproximateScoreQuery) parsedQuery).getApproximationQuery();
-        assertThat(parsedQuery, instanceOf(ApproximateQuery.class));
-        // TODO what else can we assert
+
+        // Get the exact query from ApproximateScoreQuery (which should be DateRangeIncludingNowQuery)
+        ApproximateScoreQuery approximateScoreQuery = (ApproximateScoreQuery) parsedQuery;
+        Query exactQuery = approximateScoreQuery.getOriginalQuery();
+
+        // The exact query should be DateRangeIncludingNowQuery
+        assertThat(exactQuery, instanceOf(DateRangeIncludingNowQuery.class));
+
+        ApproximateQuery approximationQuery = approximateScoreQuery.getApproximationQuery();
+        assertThat(approximationQuery, instanceOf(ApproximatePointRangeQuery.class));
+
 
         query = "{\n"
             + "    \"range\" : {\n"