Add roundtripping to PrecisionAtN

modules/rank-eval/src/main/java/org/elasticsearch/index/rankeval/PrecisionAtN.java

@@ -33,6 +33,7 @@ import java.io.IOException;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.List;
+import java.util.Objects;
 
 import javax.naming.directory.SearchResult;
 
@@ -165,10 +166,28 @@ public class PrecisionAtN extends RankedListQualityMetric<PrecisionAtN> {
 
     @Override
     public XContentBuilder toXContent(XContentBuilder builder, Params params) throws IOException {
-        builder.startObject(NAME);
+        //builder.startObject(NAME); TODO Why does roundtripping fail with the name?
+        builder.startObject();
         builder.field(SIZE_FIELD.getPreferredName(), this.n);
         builder.endObject();
         return builder;
     }
+    
+    @Override
+    public final boolean equals(Object obj) {
+        if (this == obj) {
+            return true;
+        }
+        if (obj == null || getClass() != obj.getClass()) {
+            return false;
+        }
+        PrecisionAtN other = (PrecisionAtN) obj;
+        return Objects.equals(n, other.n);
+    }
+    
+    @Override
+    public final int hashCode() {
+        return Objects.hash(getClass(), n);
+    }
 
 }

modules/rank-eval/src/test/java/org/elasticsearch/index/rankeval/PrecisionAtNTests.java

@@ -27,7 +27,6 @@ import org.elasticsearch.index.Index;
 import org.elasticsearch.index.rankeval.PrecisionAtN.Rating;
 import org.elasticsearch.search.SearchShardTarget;
 import org.elasticsearch.search.internal.InternalSearchHit;
-import org.elasticsearch.test.ESTestCase;
 
 import java.io.IOException;
 import java.util.ArrayList;
@@ -38,7 +37,7 @@ import java.util.concurrent.ExecutionException;
 
 import static java.util.Collections.emptyList;
 
-public class PrecisionAtNTests extends ESTestCase {
+public class PrecisionAtNTests extends XContentRoundtripTestCase<PrecisionAtN> {
 
     public void testPrecisionAtFiveCalculation() throws IOException, InterruptedException, ExecutionException {
         List<RatedDocument> rated = new ArrayList<>();
@@ -111,4 +110,11 @@ public class PrecisionAtNTests extends ESTestCase {
         partialResults.add(new EvalQueryQuality(0.6, emptyList()));
         assertEquals(0.3, metric.combine(partialResults), Double.MIN_VALUE);
     }
+
+    public void testXContentRoundtrip() throws IOException {
+        int position = randomIntBetween(0, 1000);
+
+        PrecisionAtN testItem = new PrecisionAtN(position);
+        roundtrip(testItem);
+    }
 }