In order to get the tests to pass again, reverted MongoDbClient to use update...

In order to get the tests to pass again, reverted MongoDbClient to use update with upsert instead of insert when batch size is 1.

mongodb/src/main/java/com/yahoo/ycsb/db/MongoDbClient.java

@@ -11,7 +11,6 @@ package com.yahoo.ycsb.db;
 
 import java.util.ArrayList;
 import java.util.HashMap;
-import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
 import java.util.Properties;
@@ -19,6 +18,7 @@ import java.util.Set;
 import java.util.Vector;
 import java.util.concurrent.atomic.AtomicInteger;
 
+import com.mongodb.client.model.Filters;
 import com.mongodb.client.model.InsertManyOptions;
 import org.bson.Document;
 import org.bson.types.Binary;
@@ -27,13 +27,10 @@ import com.mongodb.MongoClient;
 import com.mongodb.MongoClientURI;
 import com.mongodb.ReadPreference;
 import com.mongodb.WriteConcern;
-import com.mongodb.bulk.BulkWriteResult;
 import com.mongodb.client.FindIterable;
 import com.mongodb.client.MongoCollection;
 import com.mongodb.client.MongoCursor;
 import com.mongodb.client.MongoDatabase;
-import com.mongodb.client.model.BulkWriteOptions;
-import com.mongodb.client.model.InsertOneModel;
 import com.mongodb.client.model.UpdateOptions;
 import com.mongodb.client.result.DeleteResult;
 import com.mongodb.client.result.UpdateResult;
@@ -55,12 +52,16 @@ import com.yahoo.ycsb.DBException;
 public class MongoDbClient extends DB {
 
     /** Used to include a field in a response. */
-    protected static final Integer INCLUDE = Integer.valueOf(1);
+    private static final Integer INCLUDE = Integer.valueOf(1);
 
     /** The options to use for inserting many documents */
-    protected static final InsertManyOptions INSERT_UNORDERED =
+    private static final InsertManyOptions INSERT_UNORDERED =
     new InsertManyOptions().ordered(false);
 
+    /** The options to use for inserting a single document */
+    private static final UpdateOptions UPDATE_WITH_UPSERT =
+    new UpdateOptions().upsert(true);
+
     /**
      * The database name to access.
      */
@@ -244,10 +245,20 @@ public class MongoDbClient extends DB {
                 toInsert.put(entry.getKey(), entry.getValue().toArray());
             }
 
-            bulkInserts.add(toInsert);
-            if (bulkInserts.size() == batchSize) {
-                collection.insertMany(bulkInserts, INSERT_UNORDERED);
-                bulkInserts.clear();
+            if (batchSize == 1) {
+                // this is effectively an insert, but using an upsert instead due
+                // to current inability of the framework to clean up after itself
+                // between test runs.
+                collection.replaceOne(new Document("_id", toInsert.get("_id")),
+                                      toInsert,
+                                      UPDATE_WITH_UPSERT);
+            }
+            else {
+                bulkInserts.add(toInsert);
+                if (bulkInserts.size() == batchSize) {
+                    collection.insertMany(bulkInserts, INSERT_UNORDERED);
+                    bulkInserts.clear();
+                }
             }
             return 0;
         }