diff --git a/java/org/rocksdb/test/ColumnFamilyTest.java b/java/org/rocksdb/test/ColumnFamilyTest.java
index fb95e8010846ff05129ab9dfd115ce5d71e783d9..bf568b5e80580eceb3ea88b5ce854f930975586f 100644
--- a/java/org/rocksdb/test/ColumnFamilyTest.java
+++ b/java/org/rocksdb/test/ColumnFamilyTest.java
@@ -259,7 +259,8 @@ public class ColumnFamilyTest {
           new ArrayList<>();
       List<ColumnFamilyHandle> columnFamilyHandleList =
           new ArrayList<>();
-      cfNames.add(new ColumnFamilyDescriptor(RocksDB.DEFAULT_COLUMN_FAMILY));
+      cfNames.add(new ColumnFamilyDescriptor(RocksDB.DEFAULT_COLUMN_FAMILY,
+          new ColumnFamilyOptions().setMergeOperator(new StringAppendOperator())));
       cfNames.add(new ColumnFamilyDescriptor("new_cf".getBytes()));
 
       db = RocksDB.open(opt, dbFolder.getRoot().getAbsolutePath(),
@@ -268,6 +269,10 @@ public class ColumnFamilyTest {
       WriteBatch writeBatch = new WriteBatch();
       WriteOptions writeOpt = new WriteOptions();
       writeBatch.put("key".getBytes(), "value".getBytes());
+      writeBatch.put(db.getDefaultColumnFamily(),
+          "mergeKey".getBytes(), "merge".getBytes());
+      writeBatch.merge(db.getDefaultColumnFamily(), "mergeKey".getBytes(),
+          "merge".getBytes());
       writeBatch.put(columnFamilyHandleList.get(1), "newcfkey".getBytes(),
           "value".getBytes());
       writeBatch.put(columnFamilyHandleList.get(1), "newcfkey2".getBytes(),
@@ -283,6 +288,9 @@ public class ColumnFamilyTest {
       assertThat(new String(db.get(columnFamilyHandleList.get(1),
           "newcfkey2".getBytes()))).isEqualTo("value2");
       assertThat(new String(db.get("key".getBytes()))).isEqualTo("value");
+      // check if key is merged
+      assertThat(new String(db.get(db.getDefaultColumnFamily(),
+          "mergeKey".getBytes()))).isEqualTo("merge,merge");
     } finally {
       if (db != null) {
         db.close();
diff --git a/java/org/rocksdb/test/DirectSliceTest.java b/java/org/rocksdb/test/DirectSliceTest.java
index a50664867759ba021f613b35a20703c054c0037a..20a44a9041ff722bdb1fa53d9a5b108f7d916322 100644
--- a/java/org/rocksdb/test/DirectSliceTest.java
+++ b/java/org/rocksdb/test/DirectSliceTest.java
@@ -48,8 +48,10 @@ public class DirectSliceTest {
     DirectSlice directSlice = null;
     try {
       byte[] data = "Some text".getBytes();
-      ByteBuffer buffer = ByteBuffer.allocateDirect(data.length);
+      ByteBuffer buffer = ByteBuffer.allocateDirect(data.length + 1);
       buffer.put(data);
+      buffer.put(data.length, (byte)0);
+
       directSlice = new DirectSlice(buffer);
       assertThat(directSlice.toString()).isEqualTo("Some text");
     } finally {
diff --git a/java/org/rocksdb/test/FlushTest.java b/java/org/rocksdb/test/FlushTest.java
index 9dea7e753c91be4a3822554e28908dfed4aea042..3bfdb31147da87b55859cda55f9178d9d2827cd1 100644
--- a/java/org/rocksdb/test/FlushTest.java
+++ b/java/org/rocksdb/test/FlushTest.java
@@ -36,6 +36,7 @@ public class FlushTest {
       wOpt = new WriteOptions();
       flushOptions = new FlushOptions();
       flushOptions.setWaitForFlush(true);
+      assertThat(flushOptions.waitForFlush()).isTrue();
       wOpt.setDisableWAL(true);
       db = RocksDB.open(options, dbFolder.getRoot().getAbsolutePath());
       db.put(wOpt, "key1".getBytes(), "value1".getBytes());