Change Terms.Bucket to an interface (#24492)

This commit changes the Terms.Bucket abstract class to an interface, so
that it's easier for the Java High Level Rest Client to provide its own
implementation.

In its current state, the Terms.Bucket abstract class inherits from
InternalMultiBucketAggregation.InternalBucket which forces subclasses to
implement Writeable and exposes a public getProperty() method that relies
on InternalAggregation. This two points make it difficult for the Java
High Level Rest Client to implement the Terms and Terms.Bucket correctly.
This is also different from other MultiBucketsAggregation like Range
which are pure interfaces.

Changing Terms.Bucket to an interface causes a method clashes for the
`getBuckets()` method in InternalTerms. This is because:
 - InternalTerms implements Terms which declared a
 `List<Terms.Bucket> getBuckets()` method
 - InternalTerms extends InternalMultiBucketAggregation which declares a
 `List<? extends InternalBucket> getBuckets()` method
 - both overrides the MultiBucketsAggregation
 `List<? extends Bucket> getBuckets()` method

 There was no clashes before this change because Terms.Bucket extends
 InternalBucket and conformed to both declaration. With Terms.Bucket now
 an interface, the getBuckets() method in the Terms interface is changed
 to avoid method clash. This is a breaking change in the Java API but
 it's a straightforward change and the Terms multi bucket aggregation
 interface is also more coherent with the other Range, Histogram,
 Filters, AdjacencyMatrix etc that all return a `List<? extends Bucket>`.

10 files changed, 42 insertions, 40 deletions

diff --git a/core/src/test/java/org/elasticsearch/search/aggregations/bucket/DiversifiedSamplerIT.java b/core/src/test/java/org/elasticsearch/search/aggregations/bucket/DiversifiedSamplerIT.java
index 9af28806fe..c8803b7e79 100644
--- a/core/src/test/java/org/elasticsearch/search/aggregations/bucket/DiversifiedSamplerIT.java
+++ b/core/src/test/java/org/elasticsearch/search/aggregations/bucket/DiversifiedSamplerIT.java
@@ -32,6 +32,7 @@ import org.elasticsearch.search.aggregations.metrics.max.Max;
 import org.elasticsearch.test.ESIntegTestCase;
 
 import java.util.Collection;
+import java.util.List;
 
 import static org.elasticsearch.cluster.metadata.IndexMetaData.SETTING_NUMBER_OF_REPLICAS;
 import static org.elasticsearch.cluster.metadata.IndexMetaData.SETTING_NUMBER_OF_SHARDS;
@@ -108,7 +109,7 @@ public class DiversifiedSamplerIT extends ESIntegTestCase {
                 ).execute().actionGet();
         assertSearchResponse(response);
         Terms genres = response.getAggregations().get("genres");
-        Collection<Bucket> genreBuckets = genres.getBuckets();
+        Collection<? extends Bucket> genreBuckets = genres.getBuckets();
         // For this test to be useful we need >1 genre bucket to compare
         assertThat(genreBuckets.size(), greaterThan(1));
         double lastMaxPrice = asc ? Double.MIN_VALUE : Double.MAX_VALUE;
@@ -141,7 +142,7 @@ public class DiversifiedSamplerIT extends ESIntegTestCase {
         assertSearchResponse(response);
         Sampler sample = response.getAggregations().get("sample");
         Terms authors = sample.getAggregations().get("authors");
-        Collection<Bucket> testBuckets = authors.getBuckets();
+        List<? extends Bucket> testBuckets = authors.getBuckets();
 
         for (Terms.Bucket testBucket : testBuckets) {
             assertThat(testBucket.getDocCount(), lessThanOrEqualTo((long) NUM_SHARDS * MAX_DOCS_PER_AUTHOR));
@@ -162,11 +163,11 @@ public class DiversifiedSamplerIT extends ESIntegTestCase {
                 .addAggregation(rootTerms).execute().actionGet();
         assertSearchResponse(response);
         Terms genres = response.getAggregations().get("genres");
-        Collection<Bucket> genreBuckets = genres.getBuckets();
+        List<? extends Bucket> genreBuckets = genres.getBuckets();
         for (Terms.Bucket genreBucket : genreBuckets) {
             Sampler sample = genreBucket.getAggregations().get("sample");
             Terms authors = sample.getAggregations().get("authors");
-            Collection<Bucket> testBuckets = authors.getBuckets();
+            List<? extends Bucket> testBuckets = authors.getBuckets();
 
             for (Terms.Bucket testBucket : testBuckets) {
                 assertThat(testBucket.getDocCount(), lessThanOrEqualTo((long) NUM_SHARDS * MAX_DOCS_PER_AUTHOR));
@@ -195,7 +196,7 @@ public class DiversifiedSamplerIT extends ESIntegTestCase {
         Sampler sample = genreSample.getAggregations().get("sample");
 
         Terms genres = sample.getAggregations().get("genres");
-        Collection<Bucket> testBuckets = genres.getBuckets();
+        List<? extends Bucket> testBuckets = genres.getBuckets();
         for (Terms.Bucket testBucket : testBuckets) {
             assertThat(testBucket.getDocCount(), lessThanOrEqualTo((long) NUM_SHARDS * MAX_DOCS_PER_GENRE));
         }
diff --git a/core/src/test/java/org/elasticsearch/search/aggregations/bucket/DoubleTermsIT.java b/core/src/test/java/org/elasticsearch/search/aggregations/bucket/DoubleTermsIT.java
index cf28541121..ca106721fc 100644
--- a/core/src/test/java/org/elasticsearch/search/aggregations/bucket/DoubleTermsIT.java
+++ b/core/src/test/java/org/elasticsearch/search/aggregations/bucket/DoubleTermsIT.java
@@ -842,7 +842,7 @@ public class DoubleTermsIT extends AbstractTermsTestCase {
         assertThat(tags.getName(), equalTo("num_tags"));
         assertThat(tags.getBuckets().size(), equalTo(2));
 
-        Iterator<Terms.Bucket> iters = tags.getBuckets().iterator();
+        Iterator<? extends Terms.Bucket> iters = tags.getBuckets().iterator();
 
         Terms.Bucket tag = iters.next();
         assertThat(tag, notNullValue());
@@ -883,7 +883,7 @@ public class DoubleTermsIT extends AbstractTermsTestCase {
         assertThat(tags.getName(), equalTo("tags"));
         assertThat(tags.getBuckets().size(), equalTo(2));
 
-        Iterator<Terms.Bucket> iters = tags.getBuckets().iterator();
+        Iterator<? extends Terms.Bucket> iters = tags.getBuckets().iterator();
 
         // the max for "1" is 2
         // the max for "0" is 4
diff --git a/core/src/test/java/org/elasticsearch/search/aggregations/bucket/LongTermsIT.java b/core/src/test/java/org/elasticsearch/search/aggregations/bucket/LongTermsIT.java
index 6793768a91..a54dc3e2f5 100644
--- a/core/src/test/java/org/elasticsearch/search/aggregations/bucket/LongTermsIT.java
+++ b/core/src/test/java/org/elasticsearch/search/aggregations/bucket/LongTermsIT.java
@@ -854,7 +854,7 @@ public class LongTermsIT extends AbstractTermsTestCase {
         assertThat(tags.getName(), equalTo("num_tags"));
         assertThat(tags.getBuckets().size(), equalTo(2));
 
-        Iterator<Terms.Bucket> iters = tags.getBuckets().iterator();
+        Iterator<? extends Terms.Bucket> iters = tags.getBuckets().iterator();
 
         Terms.Bucket tag = iters.next();
         assertThat(tag, notNullValue());
@@ -893,7 +893,7 @@ public class LongTermsIT extends AbstractTermsTestCase {
         assertThat(tags.getName(), equalTo("tags"));
         assertThat(tags.getBuckets().size(), equalTo(2));
 
-        Iterator<Terms.Bucket> iters = tags.getBuckets().iterator();
+        Iterator<? extends Terms.Bucket> iters = tags.getBuckets().iterator();
 
         // the max for "1" is 2
         // the max for "0" is 4
diff --git a/core/src/test/java/org/elasticsearch/search/aggregations/bucket/MinDocCountIT.java b/core/src/test/java/org/elasticsearch/search/aggregations/bucket/MinDocCountIT.java
index 7307b756e3..e1e8f1ba66 100644
--- a/core/src/test/java/org/elasticsearch/search/aggregations/bucket/MinDocCountIT.java
+++ b/core/src/test/java/org/elasticsearch/search/aggregations/bucket/MinDocCountIT.java
@@ -161,8 +161,8 @@ public class MinDocCountIT extends AbstractTermsTestCase {
     // check that terms2 is a subset of terms1
     private void assertSubset(Terms terms1, Terms terms2, long minDocCount, int size, String include) {
         final Matcher matcher = include == null ? null : Pattern.compile(include).matcher("");;
-        final Iterator<Terms.Bucket> it1 = terms1.getBuckets().iterator();
-        final Iterator<Terms.Bucket> it2 = terms2.getBuckets().iterator();
+        final Iterator<? extends Terms.Bucket> it1 = terms1.getBuckets().iterator();
+        final Iterator<? extends Terms.Bucket> it2 = terms2.getBuckets().iterator();
         int size2 = 0;
         while (it1.hasNext()) {
             final Terms.Bucket bucket1 = it1.next();
diff --git a/core/src/test/java/org/elasticsearch/search/aggregations/bucket/SamplerIT.java b/core/src/test/java/org/elasticsearch/search/aggregations/bucket/SamplerIT.java
index f87b98bc87..ebd078de67 100644
--- a/core/src/test/java/org/elasticsearch/search/aggregations/bucket/SamplerIT.java
+++ b/core/src/test/java/org/elasticsearch/search/aggregations/bucket/SamplerIT.java
@@ -31,6 +31,7 @@ import org.elasticsearch.search.aggregations.metrics.max.Max;
 import org.elasticsearch.test.ESIntegTestCase;
 
 import java.util.Collection;
+import java.util.List;
 
 import static org.elasticsearch.cluster.metadata.IndexMetaData.SETTING_NUMBER_OF_REPLICAS;
 import static org.elasticsearch.cluster.metadata.IndexMetaData.SETTING_NUMBER_OF_SHARDS;
@@ -104,7 +105,7 @@ public class SamplerIT extends ESIntegTestCase {
                 ).execute().actionGet();
         assertSearchResponse(response);
         Terms genres = response.getAggregations().get("genres");
-        Collection<Bucket> genreBuckets = genres.getBuckets();
+        List<? extends Bucket> genreBuckets = genres.getBuckets();
         // For this test to be useful we need >1 genre bucket to compare
         assertThat(genreBuckets.size(), greaterThan(1));
         double lastMaxPrice = asc ? Double.MIN_VALUE : Double.MAX_VALUE;
@@ -130,7 +131,7 @@ public class SamplerIT extends ESIntegTestCase {
         assertSearchResponse(response);
         Sampler sample = response.getAggregations().get("sample");
         Terms authors = sample.getAggregations().get("authors");
-        Collection<Bucket> testBuckets = authors.getBuckets();
+        List<? extends Bucket> testBuckets = authors.getBuckets();
 
         long maxBooksPerAuthor = 0;
         for (Terms.Bucket testBucket : testBuckets) {
diff --git a/core/src/test/java/org/elasticsearch/search/aggregations/bucket/ShardSizeTermsIT.java b/core/src/test/java/org/elasticsearch/search/aggregations/bucket/ShardSizeTermsIT.java
index ecc16b85f1..748c5f886f 100644
--- a/core/src/test/java/org/elasticsearch/search/aggregations/bucket/ShardSizeTermsIT.java
+++ b/core/src/test/java/org/elasticsearch/search/aggregations/bucket/ShardSizeTermsIT.java
@@ -22,8 +22,8 @@ import org.elasticsearch.action.search.SearchResponse;
 import org.elasticsearch.search.aggregations.Aggregator.SubAggCollectionMode;
 import org.elasticsearch.search.aggregations.bucket.terms.Terms;
 
-import java.util.Collection;
 import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
 
 import static org.elasticsearch.index.query.QueryBuilders.matchAllQuery;
@@ -43,7 +43,7 @@ public class ShardSizeTermsIT extends ShardSizeTestCase {
                 .execute().actionGet();
 
         Terms  terms = response.getAggregations().get("keys");
-        Collection<Terms.Bucket> buckets = terms.getBuckets();
+        List<? extends Terms.Bucket> buckets = terms.getBuckets();
         assertThat(buckets.size(), equalTo(3));
         Map<String, Long> expected = new HashMap<>();
         expected.put("1", 8L);
@@ -66,7 +66,7 @@ public class ShardSizeTermsIT extends ShardSizeTestCase {
                 .execute().actionGet();
 
         Terms  terms = response.getAggregations().get("keys");
-        Collection<Terms.Bucket> buckets = terms.getBuckets();
+        List<? extends Terms.Bucket> buckets = terms.getBuckets();
         assertThat(buckets.size(), equalTo(3));
         Map<String, Long> expected = new HashMap<>();
         expected.put("1", 8L);
@@ -90,7 +90,7 @@ public class ShardSizeTermsIT extends ShardSizeTestCase {
                 .execute().actionGet();
 
         Terms terms = response.getAggregations().get("keys");
-        Collection<Terms.Bucket> buckets = terms.getBuckets();
+        List<? extends Terms.Bucket> buckets = terms.getBuckets();
         assertThat(buckets.size(), equalTo(3)); // we still only return 3 entries (based on the 'size' param)
         Map<String, Long> expected = new HashMap<>();
         expected.put("1", 8L);
@@ -114,7 +114,7 @@ public class ShardSizeTermsIT extends ShardSizeTestCase {
                 .execute().actionGet();
 
         Terms terms = response.getAggregations().get("keys");
-        Collection<Terms.Bucket> buckets = terms.getBuckets();
+        List<? extends Terms.Bucket> buckets = terms.getBuckets();
         assertThat(buckets.size(), equalTo(3)); // we still only return 3 entries (based on the 'size' param)
         Map<String, Long> expected = new HashMap<>();
         expected.put("1", 5L);
@@ -137,7 +137,7 @@ public class ShardSizeTermsIT extends ShardSizeTestCase {
                 .execute().actionGet();
 
         Terms  terms = response.getAggregations().get("keys");
-        Collection<Terms.Bucket> buckets = terms.getBuckets();
+        List<? extends Terms.Bucket> buckets = terms.getBuckets();
         assertThat(buckets.size(), equalTo(3));
         Map<String, Long> expected = new HashMap<>();
         expected.put("1", 8L);
@@ -160,7 +160,7 @@ public class ShardSizeTermsIT extends ShardSizeTestCase {
                 .execute().actionGet();
 
         Terms terms = response.getAggregations().get("keys");
-        Collection<Terms.Bucket> buckets = terms.getBuckets();
+        List<? extends Terms.Bucket> buckets = terms.getBuckets();
         assertThat(buckets.size(), equalTo(3));
         Map<Integer, Long> expected = new HashMap<>();
         expected.put(1, 8L);
@@ -183,7 +183,7 @@ public class ShardSizeTermsIT extends ShardSizeTestCase {
                 .execute().actionGet();
 
         Terms terms = response.getAggregations().get("keys");
-        Collection<Terms.Bucket> buckets = terms.getBuckets();
+        List<? extends Terms.Bucket> buckets = terms.getBuckets();
         assertThat(buckets.size(), equalTo(3));
         Map<Integer, Long> expected = new HashMap<>();
         expected.put(1, 8L);
@@ -206,7 +206,7 @@ public class ShardSizeTermsIT extends ShardSizeTestCase {
                 .execute().actionGet();
 
         Terms terms = response.getAggregations().get("keys");
-        Collection<Terms.Bucket> buckets = terms.getBuckets();
+        List<? extends Terms.Bucket> buckets = terms.getBuckets();
         assertThat(buckets.size(), equalTo(3)); // we still only return 3 entries (based on the 'size' param)
         Map<Integer, Long> expected = new HashMap<>();
         expected.put(1, 8L);
@@ -230,7 +230,7 @@ public class ShardSizeTermsIT extends ShardSizeTestCase {
                 .execute().actionGet();
 
         Terms terms = response.getAggregations().get("keys");
-        Collection<Terms.Bucket> buckets = terms.getBuckets();
+        List<? extends Terms.Bucket> buckets = terms.getBuckets();
         assertThat(buckets.size(), equalTo(3)); // we still only return 3 entries (based on the 'size' param)
         Map<Integer, Long> expected = new HashMap<>();
         expected.put(1, 5L);
@@ -253,7 +253,7 @@ public class ShardSizeTermsIT extends ShardSizeTestCase {
                 .execute().actionGet();
 
         Terms terms = response.getAggregations().get("keys");
-        Collection<Terms.Bucket> buckets = terms.getBuckets();
+        List<? extends Terms.Bucket> buckets = terms.getBuckets();
         assertThat(buckets.size(), equalTo(3));
         Map<Integer, Long> expected = new HashMap<>();
         expected.put(1, 8L);
@@ -276,7 +276,7 @@ public class ShardSizeTermsIT extends ShardSizeTestCase {
                 .execute().actionGet();
 
         Terms terms = response.getAggregations().get("keys");
-        Collection<Terms.Bucket> buckets = terms.getBuckets();
+        List<? extends Terms.Bucket> buckets = terms.getBuckets();
         assertThat(buckets.size(), equalTo(3));
         Map<Integer, Long> expected = new HashMap<>();
         expected.put(1, 8L);
@@ -299,7 +299,7 @@ public class ShardSizeTermsIT extends ShardSizeTestCase {
                 .execute().actionGet();
 
         Terms terms = response.getAggregations().get("keys");
-        Collection<Terms.Bucket> buckets = terms.getBuckets();
+        List<? extends Terms.Bucket> buckets = terms.getBuckets();
         assertThat(buckets.size(), equalTo(3));
         Map<Integer, Long> expected = new HashMap<>();
         expected.put(1, 8L);
@@ -322,7 +322,7 @@ public class ShardSizeTermsIT extends ShardSizeTestCase {
                 .execute().actionGet();
 
         Terms terms = response.getAggregations().get("keys");
-        Collection<Terms.Bucket> buckets = terms.getBuckets();
+        List<? extends Terms.Bucket> buckets = terms.getBuckets();
         assertThat(buckets.size(), equalTo(3));
         Map<Integer, Long> expected = new HashMap<>();
         expected.put(1, 8L);
@@ -345,7 +345,7 @@ public class ShardSizeTermsIT extends ShardSizeTestCase {
                 .execute().actionGet();
 
         Terms terms = response.getAggregations().get("keys");
-        Collection<Terms.Bucket> buckets = terms.getBuckets();
+        List<? extends Terms.Bucket> buckets = terms.getBuckets();
         assertThat(buckets.size(), equalTo(3));
         Map<Integer, Long> expected = new HashMap<>();
         expected.put(1, 5L);
@@ -368,7 +368,7 @@ public class ShardSizeTermsIT extends ShardSizeTestCase {
                 .execute().actionGet();
 
         Terms terms = response.getAggregations().get("keys");
-        Collection<Terms.Bucket> buckets = terms.getBuckets();
+        List<? extends Terms.Bucket> buckets = terms.getBuckets();
         assertThat(buckets.size(), equalTo(3));
         Map<Integer, Long> expected = new HashMap<>();
         expected.put(1, 8L);
diff --git a/core/src/test/java/org/elasticsearch/search/aggregations/bucket/SignificantTermsSignificanceScoreIT.java b/core/src/test/java/org/elasticsearch/search/aggregations/bucket/SignificantTermsSignificanceScoreIT.java
index 7fc20908e8..09cec9a458 100644
--- a/core/src/test/java/org/elasticsearch/search/aggregations/bucket/SignificantTermsSignificanceScoreIT.java
+++ b/core/src/test/java/org/elasticsearch/search/aggregations/bucket/SignificantTermsSignificanceScoreIT.java
@@ -438,7 +438,7 @@ public class SignificantTermsSignificanceScoreIT extends ESIntegTestCase {
         assertSearchResponse(response);
         StringTerms classes = response.getAggregations().get("class");
         assertThat(classes.getBuckets().size(), equalTo(2));
-        Iterator<Terms.Bucket> classBuckets = classes.getBuckets().iterator();
+        Iterator<? extends Terms.Bucket> classBuckets = classes.getBuckets().iterator();
 
         Aggregations aggregations = classBuckets.next().getAggregations();
         SignificantTerms sigTerms = aggregations.get("mySignificantTerms");
diff --git a/core/src/test/java/org/elasticsearch/search/aggregations/bucket/StringTermsIT.java b/core/src/test/java/org/elasticsearch/search/aggregations/bucket/StringTermsIT.java
index b5dbcd9085..df69cfcfa9 100644
--- a/core/src/test/java/org/elasticsearch/search/aggregations/bucket/StringTermsIT.java
+++ b/core/src/test/java/org/elasticsearch/search/aggregations/bucket/StringTermsIT.java
@@ -1012,7 +1012,7 @@ public class StringTermsIT extends AbstractTermsTestCase {
         assertThat(tags.getName(), equalTo("tags"));
         assertThat(tags.getBuckets().size(), equalTo(2));
 
-        Iterator<Terms.Bucket> iters = tags.getBuckets().iterator();
+        Iterator<? extends Terms.Bucket> iters = tags.getBuckets().iterator();
 
         Terms.Bucket tag = iters.next();
         assertThat(tag, notNullValue());
@@ -1054,7 +1054,7 @@ public class StringTermsIT extends AbstractTermsTestCase {
         assertThat(tags.getName(), equalTo("tags"));
         assertThat(tags.getBuckets().size(), equalTo(2));
 
-        Iterator<Terms.Bucket> iters = tags.getBuckets().iterator();
+        Iterator<? extends Terms.Bucket> iters = tags.getBuckets().iterator();
 
         // the max for "more" is 2
         // the max for "less" is 4
@@ -1117,7 +1117,7 @@ public class StringTermsIT extends AbstractTermsTestCase {
         assertThat(tags.getName(), equalTo("tags"));
         assertThat(tags.getBuckets().size(), equalTo(2));
 
-        Iterator<Terms.Bucket> iters = tags.getBuckets().iterator();
+        Iterator<? extends Terms.Bucket> iters = tags.getBuckets().iterator();
 
         // the max for "more" is 2
         // the max for "less" is 4
@@ -1180,7 +1180,7 @@ public class StringTermsIT extends AbstractTermsTestCase {
         assertThat(tags.getName(), equalTo("tags"));
         assertThat(tags.getBuckets().size(), equalTo(2));
 
-        Iterator<Terms.Bucket> iters = tags.getBuckets().iterator();
+        Iterator<? extends Terms.Bucket> iters = tags.getBuckets().iterator();
 
         // the max for "more" is 2
         // the max for "less" is 4
diff --git a/core/src/test/java/org/elasticsearch/search/aggregations/bucket/TermsDocCountErrorIT.java b/core/src/test/java/org/elasticsearch/search/aggregations/bucket/TermsDocCountErrorIT.java
index 9d5ca3afc5..9ed32ca2e7 100644
--- a/core/src/test/java/org/elasticsearch/search/aggregations/bucket/TermsDocCountErrorIT.java
+++ b/core/src/test/java/org/elasticsearch/search/aggregations/bucket/TermsDocCountErrorIT.java
@@ -177,7 +177,7 @@ public class TermsDocCountErrorIT extends ESIntegTestCase {
         assertThat(testTerms, notNullValue());
         assertThat(testTerms.getName(), equalTo("terms"));
         assertThat(testTerms.getDocCountError(), greaterThanOrEqualTo(0L));
-        Collection<Bucket> testBuckets = testTerms.getBuckets();
+        List<? extends Bucket> testBuckets = testTerms.getBuckets();
         assertThat(testBuckets.size(), lessThanOrEqualTo(size));
         assertThat(accurateTerms.getBuckets().size(), greaterThanOrEqualTo(testBuckets.size()));
 
@@ -211,7 +211,7 @@ public class TermsDocCountErrorIT extends ESIntegTestCase {
         assertThat(testTerms, notNullValue());
         assertThat(testTerms.getName(), equalTo("terms"));
         assertThat(testTerms.getDocCountError(), equalTo(0L));
-        Collection<Bucket> testBuckets = testTerms.getBuckets();
+        List<? extends Bucket> testBuckets = testTerms.getBuckets();
         assertThat(testBuckets.size(), lessThanOrEqualTo(size));
         assertThat(accurateTerms.getBuckets().size(), greaterThanOrEqualTo(testBuckets.size()));
 
@@ -229,7 +229,7 @@ public class TermsDocCountErrorIT extends ESIntegTestCase {
         assertThat(testTerms, notNullValue());
         assertThat(testTerms.getName(), equalTo("terms"));
         assertThat(testTerms.getDocCountError(), equalTo(0L));
-        Collection<Bucket> testBuckets = testTerms.getBuckets();
+        List<? extends Bucket> testBuckets = testTerms.getBuckets();
         assertThat(testBuckets.size(), lessThanOrEqualTo(size));
 
         for (Terms.Bucket testBucket : testBuckets) {
@@ -248,7 +248,7 @@ public class TermsDocCountErrorIT extends ESIntegTestCase {
         assertThat(testTerms, notNullValue());
         assertThat(testTerms.getName(), equalTo("terms"));
         assertThat(testTerms.getDocCountError(),anyOf(equalTo(-1L), equalTo(0L)));
-        Collection<Bucket> testBuckets = testTerms.getBuckets();
+        List<? extends Bucket> testBuckets = testTerms.getBuckets();
         assertThat(testBuckets.size(), lessThanOrEqualTo(size));
         assertThat(accurateTerms.getBuckets().size(), greaterThanOrEqualTo(testBuckets.size()));
 
@@ -988,7 +988,7 @@ public class TermsDocCountErrorIT extends ESIntegTestCase {
         Terms terms = response.getAggregations().get("terms");
         assertThat(terms, notNullValue());
         assertThat(terms.getDocCountError(), equalTo(46L));
-        List<Bucket> buckets = terms.getBuckets();
+        List<? extends Bucket> buckets = terms.getBuckets();
         assertThat(buckets, notNullValue());
         assertThat(buckets.size(), equalTo(5));
         
diff --git a/core/src/test/java/org/elasticsearch/search/aggregations/bucket/terms/TermsAggregatorTests.java b/core/src/test/java/org/elasticsearch/search/aggregations/bucket/terms/TermsAggregatorTests.java
index f2977fd769..1648d8ede9 100644
--- a/core/src/test/java/org/elasticsearch/search/aggregations/bucket/terms/TermsAggregatorTests.java
+++ b/core/src/test/java/org/elasticsearch/search/aggregations/bucket/terms/TermsAggregatorTests.java
@@ -136,7 +136,7 @@ public class TermsAggregatorTests extends AggregatorTestCase {
                 InternalAggregation mergedAggs = internalAgg.doReduce(aggs, ctx);
                 assertTrue(mergedAggs instanceof DoubleTerms);
                 long expected = numLongs + numDoubles;
-                List<Terms.Bucket> buckets = ((DoubleTerms) mergedAggs).getBuckets();
+                List<? extends Terms.Bucket> buckets = ((DoubleTerms) mergedAggs).getBuckets();
                 assertEquals(4, buckets.size());
                 assertEquals("1.0", buckets.get(0).getKeyAsString());
                 assertEquals(expected, buckets.get(0).getDocCount());