Fixup aggs test (#69476)

One of the tests that I added in #68871 worked about 99.7% of the time
but on some seeds failed to generate the right buckets because on those
seeds we would collect each segment with its own aggregator and get bad
counts. This "bad counts" problem is known in the terms aggregator - its
the price we pay for distributed work. But we can work around it either
by forcing all the docs into a single segment or by collecting all of
the buckets on the shard. We want to test the code path where don't
collect all buckets on the shard so we opt for the former.

Closes #69413

Author: nik9000

server/src/test/java/org/elasticsearch/search/aggregations/bucket/terms/TermsAggregatorTests.java

@@ -287,19 +287,27 @@ public void testStringShardMinDocCount() throws IOException {
         }
     }
 
-    public void testManyUniqueTerms() throws Exception {
+    public void testManyTerms() throws Exception {
         MappedFieldType fieldType = new KeywordFieldMapper.KeywordFieldType("string", randomBoolean(), true, null);
         TermsAggregationBuilder aggregationBuilder = new TermsAggregationBuilder("_name")
             .executionHint(randomFrom(TermsAggregatorFactory.ExecutionMode.values()).toString())
             .field("string");
         testCase(aggregationBuilder, new MatchAllDocsQuery(), iw -> {
+            /*
+             * index all of the fields into a single segment so our
+             * test gets accurate counts. We *could* set the shard size
+             * very very high but we want to test the branch of the
+             * aggregation building code that picks the top sorted aggs.
+             */
+            List<List<? extends IndexableField>> docs = new ArrayList<>();
             for (int i = 0; i < TermsAggregatorFactory.MAX_ORDS_TO_TRY_FILTERS - 200; i++) {
                 String s = String.format(Locale.ROOT, "b%03d", i);
-                iw.addDocument(doc(fieldType, s));
+                docs.add(doc(fieldType, s));
                 if (i % 100 == 7) {
-                    iw.addDocument(doc(fieldType, s));
+                    docs.add(doc(fieldType, s));
                 }
             }
+            iw.addDocuments(docs);
         }, (StringTerms result) -> {
             assertThat(
                 result.getBuckets().stream().map(StringTerms.Bucket::getKey).collect(toList()),