cadonna commented on a change in pull request #9717:
URL: https://github.com/apache/kafka/pull/9717#discussion_r566045641



##########
File path: 
streams/src/test/java/org/apache/kafka/streams/state/internals/RocksDBRangeIteratorTest.java
##########
@@ -0,0 +1,419 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.kafka.streams.state.internals;
+
+import org.apache.kafka.common.utils.Bytes;
+import org.junit.Test;
+import org.rocksdb.RocksIterator;
+
+import java.util.Collections;
+import java.util.NoSuchElementException;
+
+import static org.easymock.EasyMock.mock;
+import static org.easymock.EasyMock.expect;
+import static org.easymock.EasyMock.expectLastCall;
+import static org.easymock.EasyMock.replay;
+import static org.easymock.EasyMock.verify;
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.core.Is.is;
+import static org.junit.Assert.assertThrows;
+
+public class RocksDBRangeIteratorTest {
+
+    private final String storeName = "store";
+    private final String key1 = "a";
+    private final String key2 = "b";
+    private final String key3 = "c";
+    private final String key4 = "d";
+
+    private final String value = "value";
+    private final  Bytes key1Bytes = Bytes.wrap(key1.getBytes());
+    private final  Bytes key2Bytes = Bytes.wrap(key2.getBytes());
+    private final  Bytes key3Bytes = Bytes.wrap(key3.getBytes());
+    private final  Bytes key4Bytes = Bytes.wrap(key4.getBytes());
+    private final byte[] valueBytes = value.getBytes();
+
+    @Test
+    public void shouldReturnAllKeysInTheRangeInForwardDirection() {
+
+        final RocksIterator rocksIterator = mock(RocksIterator.class);
+        rocksIterator.seek(key1Bytes.get());
+        expect(rocksIterator.isValid())
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(false);
+        expect(rocksIterator.key())
+            .andReturn(key1Bytes.get())
+            .andReturn(key2Bytes.get())
+            .andReturn(key3Bytes.get());
+        expect(rocksIterator.value()).andReturn(valueBytes).times(3);
+        rocksIterator.next();
+        expectLastCall().times(3);
+        replay(rocksIterator);
+        final RocksDBRangeIterator rocksDBRangeIterator = new 
RocksDBRangeIterator(
+                storeName,
+            rocksIterator,
+            Collections.emptySet(),
+            key1Bytes,
+            key3Bytes,
+            true
+        );

Review comment:
       ```suggestion
           final RocksDBRangeIterator rocksDBRangeIterator = new 
RocksDBRangeIterator(
               storeName,
               rocksIterator,
               Collections.emptySet(),
               key1Bytes,
               key3Bytes,
               true
           );
   ```
   Please also fix the other wrong indentations.

##########
File path: 
streams/src/test/java/org/apache/kafka/streams/state/internals/RocksDBRangeIteratorTest.java
##########
@@ -0,0 +1,419 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.kafka.streams.state.internals;
+
+import org.apache.kafka.common.utils.Bytes;
+import org.junit.Test;
+import org.rocksdb.RocksIterator;
+
+import java.util.Collections;
+import java.util.NoSuchElementException;
+
+import static org.easymock.EasyMock.mock;
+import static org.easymock.EasyMock.expect;
+import static org.easymock.EasyMock.expectLastCall;
+import static org.easymock.EasyMock.replay;
+import static org.easymock.EasyMock.verify;
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.core.Is.is;
+import static org.junit.Assert.assertThrows;
+
+public class RocksDBRangeIteratorTest {
+
+    private final String storeName = "store";
+    private final String key1 = "a";
+    private final String key2 = "b";
+    private final String key3 = "c";
+    private final String key4 = "d";
+
+    private final String value = "value";
+    private final  Bytes key1Bytes = Bytes.wrap(key1.getBytes());
+    private final  Bytes key2Bytes = Bytes.wrap(key2.getBytes());
+    private final  Bytes key3Bytes = Bytes.wrap(key3.getBytes());
+    private final  Bytes key4Bytes = Bytes.wrap(key4.getBytes());
+    private final byte[] valueBytes = value.getBytes();
+
+    @Test
+    public void shouldReturnAllKeysInTheRangeInForwardDirection() {
+
+        final RocksIterator rocksIterator = mock(RocksIterator.class);
+        rocksIterator.seek(key1Bytes.get());
+        expect(rocksIterator.isValid())
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(false);
+        expect(rocksIterator.key())
+            .andReturn(key1Bytes.get())
+            .andReturn(key2Bytes.get())
+            .andReturn(key3Bytes.get());
+        expect(rocksIterator.value()).andReturn(valueBytes).times(3);
+        rocksIterator.next();
+        expectLastCall().times(3);
+        replay(rocksIterator);
+        final RocksDBRangeIterator rocksDBRangeIterator = new 
RocksDBRangeIterator(
+                storeName,
+            rocksIterator,
+            Collections.emptySet(),
+            key1Bytes,
+            key3Bytes,
+            true
+        );
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key1Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key2Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key3Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(false));
+        verify(rocksIterator);
+    }
+
+    @Test
+    public void shouldReturnAllKeysInTheRangeReverseDirection() {
+
+        final RocksIterator rocksIterator = mock(RocksIterator.class);
+        rocksIterator.seekForPrev(key3Bytes.get());
+        expect(rocksIterator.isValid())
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(false);
+        expect(rocksIterator.key())
+            .andReturn(key3Bytes.get())
+            .andReturn(key2Bytes.get())
+            .andReturn(key1Bytes.get());
+        expect(rocksIterator.value()).andReturn(valueBytes).times(3);
+        rocksIterator.prev();
+        expectLastCall().times(3);
+        replay(rocksIterator);
+        final RocksDBRangeIterator rocksDBRangeIterator = new 
RocksDBRangeIterator(
+                storeName,
+            rocksIterator,
+            Collections.emptySet(),
+            key1Bytes,
+            key3Bytes,
+            false
+        );
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key3Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key2Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key1Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(false));
+        verify(rocksIterator);
+    }
+
+    @Test
+    public void 
shouldReturnAllKeysWhenLastKeyIsGreaterThanLargestKeyInStateStoreInForwardDirection()
 {
+
+        final String to = "f";
+        final  Bytes toBytes = Bytes.wrap(to.getBytes());
+        final RocksIterator rocksIterator = mock(RocksIterator.class);
+        rocksIterator.seek(key1Bytes.get());
+        expect(rocksIterator.isValid())
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(false);
+        expect(rocksIterator.key())
+            .andReturn(key1Bytes.get())
+            .andReturn(key2Bytes.get())
+            .andReturn(key3Bytes.get())
+            .andReturn(key4Bytes.get());
+        expect(rocksIterator.value()).andReturn(valueBytes).times(4);
+        rocksIterator.next();
+        expectLastCall().times(4);
+        replay(rocksIterator);
+        final RocksDBRangeIterator rocksDBRangeIterator = new 
RocksDBRangeIterator(
+                storeName,
+            rocksIterator,
+            Collections.emptySet(),
+            key1Bytes,
+            toBytes,
+            true
+        );
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key1Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key2Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key3Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key4Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(false));
+        verify(rocksIterator);
+    }
+
+
+    @Test
+    public void 
shouldReturnAllKeysWhenLastKeyIsSmallerThanSmallestKeyInStateStoreInReverseDirection()
 {
+        final String to = "a";
+        final  Bytes toBytes = Bytes.wrap(to.getBytes());
+
+        final RocksIterator rocksIterator = mock(RocksIterator.class);
+        rocksIterator.seekForPrev(key4Bytes.get());
+        expect(rocksIterator.isValid())
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(false);
+        expect(rocksIterator.key())
+            .andReturn(key4Bytes.get())
+            .andReturn(key3Bytes.get())
+            .andReturn(key2Bytes.get())
+            .andReturn(key1Bytes.get());
+        expect(rocksIterator.value()).andReturn(valueBytes).times(4);
+        rocksIterator.prev();
+        expectLastCall().times(4);
+        replay(rocksIterator);
+        final RocksDBRangeIterator rocksDBRangeIterator = new 
RocksDBRangeIterator(
+                storeName,
+            rocksIterator,
+            Collections.emptySet(),
+            toBytes,
+            key4Bytes,
+            false
+        );
+
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key4Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key3Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key2Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key1Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(false));
+        verify(rocksIterator);
+    }
+
+
+    @Test
+    public void 
shouldReturnNoKeysWhenLastKeyIsSmallerThanSmallestKeyInStateStoreForwardDirection()
 {
+
+        // key range in state store: [c-f]
+
+        final RocksIterator rocksIterator = mock(RocksIterator.class);
+        rocksIterator.seek(key1Bytes.get());
+        expect(rocksIterator.isValid())
+            .andReturn(false);
+

Review comment:
       ```suggestion
           expect(rocksIterator.isValid()).andReturn(false);
   ```

##########
File path: 
streams/src/test/java/org/apache/kafka/streams/state/internals/RocksDBRangeIteratorTest.java
##########
@@ -0,0 +1,419 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.kafka.streams.state.internals;
+
+import org.apache.kafka.common.utils.Bytes;
+import org.junit.Test;
+import org.rocksdb.RocksIterator;
+
+import java.util.Collections;
+import java.util.NoSuchElementException;
+
+import static org.easymock.EasyMock.mock;
+import static org.easymock.EasyMock.expect;
+import static org.easymock.EasyMock.expectLastCall;
+import static org.easymock.EasyMock.replay;
+import static org.easymock.EasyMock.verify;
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.core.Is.is;
+import static org.junit.Assert.assertThrows;
+
+public class RocksDBRangeIteratorTest {
+
+    private final String storeName = "store";
+    private final String key1 = "a";
+    private final String key2 = "b";
+    private final String key3 = "c";
+    private final String key4 = "d";
+
+    private final String value = "value";
+    private final  Bytes key1Bytes = Bytes.wrap(key1.getBytes());
+    private final  Bytes key2Bytes = Bytes.wrap(key2.getBytes());
+    private final  Bytes key3Bytes = Bytes.wrap(key3.getBytes());
+    private final  Bytes key4Bytes = Bytes.wrap(key4.getBytes());
+    private final byte[] valueBytes = value.getBytes();
+
+    @Test
+    public void shouldReturnAllKeysInTheRangeInForwardDirection() {
+
+        final RocksIterator rocksIterator = mock(RocksIterator.class);
+        rocksIterator.seek(key1Bytes.get());
+        expect(rocksIterator.isValid())
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(false);
+        expect(rocksIterator.key())
+            .andReturn(key1Bytes.get())
+            .andReturn(key2Bytes.get())
+            .andReturn(key3Bytes.get());
+        expect(rocksIterator.value()).andReturn(valueBytes).times(3);
+        rocksIterator.next();
+        expectLastCall().times(3);
+        replay(rocksIterator);
+        final RocksDBRangeIterator rocksDBRangeIterator = new 
RocksDBRangeIterator(
+                storeName,
+            rocksIterator,
+            Collections.emptySet(),
+            key1Bytes,
+            key3Bytes,
+            true
+        );
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key1Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key2Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key3Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(false));
+        verify(rocksIterator);
+    }
+
+    @Test
+    public void shouldReturnAllKeysInTheRangeReverseDirection() {
+
+        final RocksIterator rocksIterator = mock(RocksIterator.class);
+        rocksIterator.seekForPrev(key3Bytes.get());
+        expect(rocksIterator.isValid())
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(false);
+        expect(rocksIterator.key())
+            .andReturn(key3Bytes.get())
+            .andReturn(key2Bytes.get())
+            .andReturn(key1Bytes.get());
+        expect(rocksIterator.value()).andReturn(valueBytes).times(3);
+        rocksIterator.prev();
+        expectLastCall().times(3);
+        replay(rocksIterator);
+        final RocksDBRangeIterator rocksDBRangeIterator = new 
RocksDBRangeIterator(
+                storeName,
+            rocksIterator,
+            Collections.emptySet(),
+            key1Bytes,
+            key3Bytes,
+            false
+        );
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key3Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key2Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key1Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(false));
+        verify(rocksIterator);
+    }
+
+    @Test
+    public void 
shouldReturnAllKeysWhenLastKeyIsGreaterThanLargestKeyInStateStoreInForwardDirection()
 {
+
+        final String to = "f";
+        final  Bytes toBytes = Bytes.wrap(to.getBytes());
+        final RocksIterator rocksIterator = mock(RocksIterator.class);
+        rocksIterator.seek(key1Bytes.get());
+        expect(rocksIterator.isValid())
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(false);
+        expect(rocksIterator.key())
+            .andReturn(key1Bytes.get())
+            .andReturn(key2Bytes.get())
+            .andReturn(key3Bytes.get())
+            .andReturn(key4Bytes.get());
+        expect(rocksIterator.value()).andReturn(valueBytes).times(4);
+        rocksIterator.next();
+        expectLastCall().times(4);
+        replay(rocksIterator);
+        final RocksDBRangeIterator rocksDBRangeIterator = new 
RocksDBRangeIterator(
+                storeName,
+            rocksIterator,
+            Collections.emptySet(),
+            key1Bytes,
+            toBytes,
+            true
+        );
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key1Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key2Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key3Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key4Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(false));
+        verify(rocksIterator);
+    }
+
+
+    @Test
+    public void 
shouldReturnAllKeysWhenLastKeyIsSmallerThanSmallestKeyInStateStoreInReverseDirection()
 {
+        final String to = "a";
+        final  Bytes toBytes = Bytes.wrap(to.getBytes());
+
+        final RocksIterator rocksIterator = mock(RocksIterator.class);
+        rocksIterator.seekForPrev(key4Bytes.get());
+        expect(rocksIterator.isValid())
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(false);
+        expect(rocksIterator.key())
+            .andReturn(key4Bytes.get())
+            .andReturn(key3Bytes.get())
+            .andReturn(key2Bytes.get())
+            .andReturn(key1Bytes.get());
+        expect(rocksIterator.value()).andReturn(valueBytes).times(4);
+        rocksIterator.prev();
+        expectLastCall().times(4);
+        replay(rocksIterator);
+        final RocksDBRangeIterator rocksDBRangeIterator = new 
RocksDBRangeIterator(
+                storeName,
+            rocksIterator,
+            Collections.emptySet(),
+            toBytes,
+            key4Bytes,
+            false
+        );
+
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key4Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key3Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key2Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key1Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(false));
+        verify(rocksIterator);
+    }
+
+
+    @Test
+    public void 
shouldReturnNoKeysWhenLastKeyIsSmallerThanSmallestKeyInStateStoreForwardDirection()
 {
+
+        // key range in state store: [c-f]
+
+        final RocksIterator rocksIterator = mock(RocksIterator.class);
+        rocksIterator.seek(key1Bytes.get());
+        expect(rocksIterator.isValid())
+            .andReturn(false);
+
+        replay(rocksIterator);
+        final RocksDBRangeIterator rocksDBRangeIterator = new 
RocksDBRangeIterator(
+                storeName,
+            rocksIterator,
+            Collections.emptySet(),
+            key1Bytes,
+            key2Bytes,
+            true
+        );
+        assertThat(rocksDBRangeIterator.hasNext(), is(false));
+        verify(rocksIterator);
+
+    }
+
+    @Test
+    public void 
shouldReturnNoKeysWhenLastKeyIsLargerThanLargestKeyInStateStoreReverseDirection()
 {
+
+        // key range in state store: [c-f]
+        final String from = "g";
+        final String to = "h";
+
+        final  Bytes fromBytes = Bytes.wrap(from.getBytes());
+        final  Bytes toBytes = Bytes.wrap(to.getBytes());
+        final RocksIterator rocksIterator = mock(RocksIterator.class);
+        rocksIterator.seekForPrev(toBytes.get());
+        expect(rocksIterator.isValid())
+            .andReturn(false);
+
+        replay(rocksIterator);
+        final RocksDBRangeIterator rocksDBRangeIterator = new 
RocksDBRangeIterator(
+                storeName,
+            rocksIterator,
+            Collections.emptySet(),
+            fromBytes,
+            toBytes,
+            false
+        );
+        assertThat(rocksDBRangeIterator.hasNext(), is(false));
+        verify(rocksIterator);
+    }
+
+    @Test
+    public void 
shouldReturnAllKeysInPartiallyOverlappingRangeInForwardDirection() {
+
+        final RocksIterator rocksIterator = mock(RocksIterator.class);
+        rocksIterator.seek(key1Bytes.get());
+        expect(rocksIterator.isValid())
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(false);
+        expect(rocksIterator.key())
+            .andReturn(key2Bytes.get())
+            .andReturn(key3Bytes.get());
+        expect(rocksIterator.value()).andReturn(valueBytes).times(2);
+        rocksIterator.next();
+        expectLastCall().times(2);
+        replay(rocksIterator);
+        final RocksDBRangeIterator rocksDBRangeIterator = new 
RocksDBRangeIterator(
+                storeName,
+            rocksIterator,
+            Collections.emptySet(),
+            key1Bytes,
+            key3Bytes,
+            true
+        );
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key2Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key3Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(false));
+        verify(rocksIterator);
+    }
+
+    @Test
+    public void 
shouldReturnAllKeysInPartiallyOverlappingRangeInReverseDirection() {
+
+        final RocksIterator rocksIterator = mock(RocksIterator.class);
+        final String to = "e";
+        final Bytes toBytes = Bytes.wrap(to.getBytes());
+        rocksIterator.seekForPrev(toBytes.get());
+        expect(rocksIterator.isValid())
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(false);
+        expect(rocksIterator.key())
+            .andReturn(key4Bytes.get())
+            .andReturn(key3Bytes.get());
+        expect(rocksIterator.value()).andReturn(valueBytes).times(2);
+        rocksIterator.prev();
+        expectLastCall().times(2);
+        replay(rocksIterator);
+        final RocksDBRangeIterator rocksDBRangeIterator = new 
RocksDBRangeIterator(
+                storeName,
+            rocksIterator,
+            Collections.emptySet(),
+            key3Bytes,
+            toBytes,
+            false
+        );
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key4Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key3Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(false));
+        verify(rocksIterator);
+    }
+
+    @Test
+    public void 
shouldReturnTheCurrentKeyOnInvokingPeekNextKeyInForwardDirection() {
+        final RocksIterator rocksIterator = mock(RocksIterator.class);
+        rocksIterator.seek(key1Bytes.get());
+        expect(rocksIterator.isValid())
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(false);
+        expect(rocksIterator.key())
+            .andReturn(key2Bytes.get())
+            .andReturn(key3Bytes.get());
+        expect(rocksIterator.value()).andReturn(valueBytes).times(2);
+        rocksIterator.next();
+        expectLastCall().times(2);
+        replay(rocksIterator);
+        final RocksDBRangeIterator rocksDBRangeIterator = new 
RocksDBRangeIterator(
+                storeName,
+            rocksIterator,
+            Collections.emptySet(),
+            key1Bytes,
+            key3Bytes,
+            true
+        );
+
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.peekNextKey(), is(key2Bytes));
+        assertThat(rocksDBRangeIterator.next().key, is(key2Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.peekNextKey(), is(key3Bytes));
+        assertThat(rocksDBRangeIterator.next().key, is(key3Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(false));
+        assertThrows(NoSuchElementException.class, 
rocksDBRangeIterator::peekNextKey);
+        verify(rocksIterator);
+    }
+
+    @Test
+    public void 
shouldReturnTheCurrentKeyOnInvokingPeekNextKeyInReverseDirection() {
+        final RocksIterator rocksIterator = mock(RocksIterator.class);
+        final String to = "e";
+        final Bytes toBytes = Bytes.wrap(to.getBytes());
+        rocksIterator.seekForPrev(toBytes.get());
+        expect(rocksIterator.isValid())
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(false);
+        expect(rocksIterator.key())
+            .andReturn(key4Bytes.get())
+            .andReturn(key3Bytes.get());
+        expect(rocksIterator.value()).andReturn(valueBytes).times(2);
+        rocksIterator.prev();
+        expectLastCall().times(2);
+        replay(rocksIterator);
+        final RocksDBRangeIterator rocksDBRangeIterator = new 
RocksDBRangeIterator(
+                storeName,
+            rocksIterator,
+            Collections.emptySet(),
+            key3Bytes,
+            toBytes,
+            false
+        );
+
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.peekNextKey(), is(key4Bytes));
+        assertThat(rocksDBRangeIterator.next().key, is(key4Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.peekNextKey(), is(key3Bytes));
+        assertThat(rocksDBRangeIterator.next().key, is(key3Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(false));
+        assertThrows(NoSuchElementException.class, 
rocksDBRangeIterator::peekNextKey);
+        verify(rocksIterator);
+    }
+
+    @Test
+    public void testCloseIterator() {

Review comment:
       Please rename to `shouldCloseIterator()`.

##########
File path: 
streams/src/test/java/org/apache/kafka/streams/state/internals/RocksDBRangeIteratorTest.java
##########
@@ -0,0 +1,419 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.kafka.streams.state.internals;
+
+import org.apache.kafka.common.utils.Bytes;
+import org.junit.Test;
+import org.rocksdb.RocksIterator;
+
+import java.util.Collections;
+import java.util.NoSuchElementException;
+
+import static org.easymock.EasyMock.mock;
+import static org.easymock.EasyMock.expect;
+import static org.easymock.EasyMock.expectLastCall;
+import static org.easymock.EasyMock.replay;
+import static org.easymock.EasyMock.verify;
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.core.Is.is;
+import static org.junit.Assert.assertThrows;
+
+public class RocksDBRangeIteratorTest {
+
+    private final String storeName = "store";
+    private final String key1 = "a";
+    private final String key2 = "b";
+    private final String key3 = "c";
+    private final String key4 = "d";
+
+    private final String value = "value";
+    private final  Bytes key1Bytes = Bytes.wrap(key1.getBytes());
+    private final  Bytes key2Bytes = Bytes.wrap(key2.getBytes());
+    private final  Bytes key3Bytes = Bytes.wrap(key3.getBytes());
+    private final  Bytes key4Bytes = Bytes.wrap(key4.getBytes());
+    private final byte[] valueBytes = value.getBytes();
+
+    @Test
+    public void shouldReturnAllKeysInTheRangeInForwardDirection() {
+
+        final RocksIterator rocksIterator = mock(RocksIterator.class);
+        rocksIterator.seek(key1Bytes.get());
+        expect(rocksIterator.isValid())
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(false);
+        expect(rocksIterator.key())
+            .andReturn(key1Bytes.get())
+            .andReturn(key2Bytes.get())
+            .andReturn(key3Bytes.get());
+        expect(rocksIterator.value()).andReturn(valueBytes).times(3);
+        rocksIterator.next();
+        expectLastCall().times(3);
+        replay(rocksIterator);
+        final RocksDBRangeIterator rocksDBRangeIterator = new 
RocksDBRangeIterator(
+                storeName,
+            rocksIterator,
+            Collections.emptySet(),
+            key1Bytes,
+            key3Bytes,
+            true
+        );
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key1Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key2Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key3Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(false));
+        verify(rocksIterator);
+    }
+
+    @Test
+    public void shouldReturnAllKeysInTheRangeReverseDirection() {
+
+        final RocksIterator rocksIterator = mock(RocksIterator.class);
+        rocksIterator.seekForPrev(key3Bytes.get());
+        expect(rocksIterator.isValid())
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(false);
+        expect(rocksIterator.key())
+            .andReturn(key3Bytes.get())
+            .andReturn(key2Bytes.get())
+            .andReturn(key1Bytes.get());
+        expect(rocksIterator.value()).andReturn(valueBytes).times(3);
+        rocksIterator.prev();
+        expectLastCall().times(3);
+        replay(rocksIterator);
+        final RocksDBRangeIterator rocksDBRangeIterator = new 
RocksDBRangeIterator(
+                storeName,
+            rocksIterator,
+            Collections.emptySet(),
+            key1Bytes,
+            key3Bytes,
+            false
+        );
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key3Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key2Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key1Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(false));
+        verify(rocksIterator);
+    }
+
+    @Test
+    public void 
shouldReturnAllKeysWhenLastKeyIsGreaterThanLargestKeyInStateStoreInForwardDirection()
 {
+
+        final String to = "f";
+        final  Bytes toBytes = Bytes.wrap(to.getBytes());
+        final RocksIterator rocksIterator = mock(RocksIterator.class);
+        rocksIterator.seek(key1Bytes.get());
+        expect(rocksIterator.isValid())
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(false);
+        expect(rocksIterator.key())
+            .andReturn(key1Bytes.get())
+            .andReturn(key2Bytes.get())
+            .andReturn(key3Bytes.get())
+            .andReturn(key4Bytes.get());
+        expect(rocksIterator.value()).andReturn(valueBytes).times(4);
+        rocksIterator.next();
+        expectLastCall().times(4);
+        replay(rocksIterator);
+        final RocksDBRangeIterator rocksDBRangeIterator = new 
RocksDBRangeIterator(
+                storeName,
+            rocksIterator,
+            Collections.emptySet(),
+            key1Bytes,
+            toBytes,
+            true
+        );
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key1Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key2Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key3Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key4Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(false));
+        verify(rocksIterator);
+    }
+
+
+    @Test
+    public void 
shouldReturnAllKeysWhenLastKeyIsSmallerThanSmallestKeyInStateStoreInReverseDirection()
 {
+        final String to = "a";
+        final  Bytes toBytes = Bytes.wrap(to.getBytes());
+
+        final RocksIterator rocksIterator = mock(RocksIterator.class);
+        rocksIterator.seekForPrev(key4Bytes.get());
+        expect(rocksIterator.isValid())
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(false);
+        expect(rocksIterator.key())
+            .andReturn(key4Bytes.get())
+            .andReturn(key3Bytes.get())
+            .andReturn(key2Bytes.get())
+            .andReturn(key1Bytes.get());
+        expect(rocksIterator.value()).andReturn(valueBytes).times(4);
+        rocksIterator.prev();
+        expectLastCall().times(4);
+        replay(rocksIterator);
+        final RocksDBRangeIterator rocksDBRangeIterator = new 
RocksDBRangeIterator(
+                storeName,
+            rocksIterator,
+            Collections.emptySet(),
+            toBytes,
+            key4Bytes,
+            false
+        );
+
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key4Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key3Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key2Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key1Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(false));
+        verify(rocksIterator);
+    }
+
+
+    @Test
+    public void 
shouldReturnNoKeysWhenLastKeyIsSmallerThanSmallestKeyInStateStoreForwardDirection()
 {
+
+        // key range in state store: [c-f]
+
+        final RocksIterator rocksIterator = mock(RocksIterator.class);
+        rocksIterator.seek(key1Bytes.get());
+        expect(rocksIterator.isValid())
+            .andReturn(false);
+
+        replay(rocksIterator);
+        final RocksDBRangeIterator rocksDBRangeIterator = new 
RocksDBRangeIterator(
+                storeName,
+            rocksIterator,
+            Collections.emptySet(),
+            key1Bytes,
+            key2Bytes,
+            true
+        );
+        assertThat(rocksDBRangeIterator.hasNext(), is(false));
+        verify(rocksIterator);
+
+    }
+
+    @Test
+    public void 
shouldReturnNoKeysWhenLastKeyIsLargerThanLargestKeyInStateStoreReverseDirection()
 {
+
+        // key range in state store: [c-f]
+        final String from = "g";
+        final String to = "h";
+
+        final  Bytes fromBytes = Bytes.wrap(from.getBytes());
+        final  Bytes toBytes = Bytes.wrap(to.getBytes());
+        final RocksIterator rocksIterator = mock(RocksIterator.class);
+        rocksIterator.seekForPrev(toBytes.get());
+        expect(rocksIterator.isValid())
+            .andReturn(false);
+
+        replay(rocksIterator);
+        final RocksDBRangeIterator rocksDBRangeIterator = new 
RocksDBRangeIterator(
+                storeName,
+            rocksIterator,
+            Collections.emptySet(),
+            fromBytes,
+            toBytes,
+            false
+        );
+        assertThat(rocksDBRangeIterator.hasNext(), is(false));
+        verify(rocksIterator);
+    }
+
+    @Test
+    public void 
shouldReturnAllKeysInPartiallyOverlappingRangeInForwardDirection() {
+
+        final RocksIterator rocksIterator = mock(RocksIterator.class);
+        rocksIterator.seek(key1Bytes.get());
+        expect(rocksIterator.isValid())
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(false);
+        expect(rocksIterator.key())
+            .andReturn(key2Bytes.get())
+            .andReturn(key3Bytes.get());
+        expect(rocksIterator.value()).andReturn(valueBytes).times(2);
+        rocksIterator.next();
+        expectLastCall().times(2);
+        replay(rocksIterator);
+        final RocksDBRangeIterator rocksDBRangeIterator = new 
RocksDBRangeIterator(
+                storeName,
+            rocksIterator,
+            Collections.emptySet(),
+            key1Bytes,
+            key3Bytes,
+            true
+        );
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key2Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key3Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(false));
+        verify(rocksIterator);
+    }
+
+    @Test
+    public void 
shouldReturnAllKeysInPartiallyOverlappingRangeInReverseDirection() {
+
+        final RocksIterator rocksIterator = mock(RocksIterator.class);
+        final String to = "e";
+        final Bytes toBytes = Bytes.wrap(to.getBytes());
+        rocksIterator.seekForPrev(toBytes.get());
+        expect(rocksIterator.isValid())
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(false);
+        expect(rocksIterator.key())
+            .andReturn(key4Bytes.get())
+            .andReturn(key3Bytes.get());
+        expect(rocksIterator.value()).andReturn(valueBytes).times(2);
+        rocksIterator.prev();
+        expectLastCall().times(2);
+        replay(rocksIterator);
+        final RocksDBRangeIterator rocksDBRangeIterator = new 
RocksDBRangeIterator(
+                storeName,
+            rocksIterator,
+            Collections.emptySet(),
+            key3Bytes,
+            toBytes,
+            false
+        );
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key4Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key3Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(false));
+        verify(rocksIterator);
+    }
+
+    @Test
+    public void 
shouldReturnTheCurrentKeyOnInvokingPeekNextKeyInForwardDirection() {
+        final RocksIterator rocksIterator = mock(RocksIterator.class);
+        rocksIterator.seek(key1Bytes.get());
+        expect(rocksIterator.isValid())
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(false);
+        expect(rocksIterator.key())
+            .andReturn(key2Bytes.get())
+            .andReturn(key3Bytes.get());
+        expect(rocksIterator.value()).andReturn(valueBytes).times(2);
+        rocksIterator.next();
+        expectLastCall().times(2);
+        replay(rocksIterator);
+        final RocksDBRangeIterator rocksDBRangeIterator = new 
RocksDBRangeIterator(
+                storeName,
+            rocksIterator,
+            Collections.emptySet(),
+            key1Bytes,
+            key3Bytes,
+            true
+        );
+
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.peekNextKey(), is(key2Bytes));
+        assertThat(rocksDBRangeIterator.next().key, is(key2Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.peekNextKey(), is(key3Bytes));
+        assertThat(rocksDBRangeIterator.next().key, is(key3Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(false));
+        assertThrows(NoSuchElementException.class, 
rocksDBRangeIterator::peekNextKey);
+        verify(rocksIterator);
+    }
+
+    @Test
+    public void 
shouldReturnTheCurrentKeyOnInvokingPeekNextKeyInReverseDirection() {
+        final RocksIterator rocksIterator = mock(RocksIterator.class);
+        final String to = "e";
+        final Bytes toBytes = Bytes.wrap(to.getBytes());
+        rocksIterator.seekForPrev(toBytes.get());
+        expect(rocksIterator.isValid())
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(false);
+        expect(rocksIterator.key())
+            .andReturn(key4Bytes.get())
+            .andReturn(key3Bytes.get());
+        expect(rocksIterator.value()).andReturn(valueBytes).times(2);
+        rocksIterator.prev();
+        expectLastCall().times(2);
+        replay(rocksIterator);
+        final RocksDBRangeIterator rocksDBRangeIterator = new 
RocksDBRangeIterator(
+                storeName,
+            rocksIterator,
+            Collections.emptySet(),
+            key3Bytes,
+            toBytes,
+            false
+        );
+
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.peekNextKey(), is(key4Bytes));
+        assertThat(rocksDBRangeIterator.next().key, is(key4Bytes));

Review comment:
       See my comment above.

##########
File path: 
streams/src/test/java/org/apache/kafka/streams/state/internals/RocksDBRangeIteratorTest.java
##########
@@ -0,0 +1,419 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.kafka.streams.state.internals;
+
+import org.apache.kafka.common.utils.Bytes;
+import org.junit.Test;
+import org.rocksdb.RocksIterator;
+
+import java.util.Collections;
+import java.util.NoSuchElementException;
+
+import static org.easymock.EasyMock.mock;
+import static org.easymock.EasyMock.expect;
+import static org.easymock.EasyMock.expectLastCall;
+import static org.easymock.EasyMock.replay;
+import static org.easymock.EasyMock.verify;
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.core.Is.is;
+import static org.junit.Assert.assertThrows;
+
+public class RocksDBRangeIteratorTest {
+
+    private final String storeName = "store";
+    private final String key1 = "a";
+    private final String key2 = "b";
+    private final String key3 = "c";
+    private final String key4 = "d";
+
+    private final String value = "value";
+    private final  Bytes key1Bytes = Bytes.wrap(key1.getBytes());
+    private final  Bytes key2Bytes = Bytes.wrap(key2.getBytes());
+    private final  Bytes key3Bytes = Bytes.wrap(key3.getBytes());
+    private final  Bytes key4Bytes = Bytes.wrap(key4.getBytes());
+    private final byte[] valueBytes = value.getBytes();
+
+    @Test
+    public void shouldReturnAllKeysInTheRangeInForwardDirection() {
+
+        final RocksIterator rocksIterator = mock(RocksIterator.class);
+        rocksIterator.seek(key1Bytes.get());
+        expect(rocksIterator.isValid())
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(false);
+        expect(rocksIterator.key())
+            .andReturn(key1Bytes.get())
+            .andReturn(key2Bytes.get())
+            .andReturn(key3Bytes.get());
+        expect(rocksIterator.value()).andReturn(valueBytes).times(3);
+        rocksIterator.next();
+        expectLastCall().times(3);
+        replay(rocksIterator);
+        final RocksDBRangeIterator rocksDBRangeIterator = new 
RocksDBRangeIterator(
+                storeName,
+            rocksIterator,
+            Collections.emptySet(),
+            key1Bytes,
+            key3Bytes,
+            true
+        );
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key1Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key2Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key3Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(false));
+        verify(rocksIterator);
+    }
+
+    @Test
+    public void shouldReturnAllKeysInTheRangeReverseDirection() {
+
+        final RocksIterator rocksIterator = mock(RocksIterator.class);
+        rocksIterator.seekForPrev(key3Bytes.get());
+        expect(rocksIterator.isValid())
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(false);
+        expect(rocksIterator.key())
+            .andReturn(key3Bytes.get())
+            .andReturn(key2Bytes.get())
+            .andReturn(key1Bytes.get());
+        expect(rocksIterator.value()).andReturn(valueBytes).times(3);
+        rocksIterator.prev();
+        expectLastCall().times(3);
+        replay(rocksIterator);
+        final RocksDBRangeIterator rocksDBRangeIterator = new 
RocksDBRangeIterator(
+                storeName,
+            rocksIterator,
+            Collections.emptySet(),
+            key1Bytes,
+            key3Bytes,
+            false
+        );
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key3Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key2Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key1Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(false));
+        verify(rocksIterator);
+    }
+
+    @Test
+    public void 
shouldReturnAllKeysWhenLastKeyIsGreaterThanLargestKeyInStateStoreInForwardDirection()
 {
+
+        final String to = "f";
+        final  Bytes toBytes = Bytes.wrap(to.getBytes());

Review comment:
       ```suggestion
           final Bytes toBytes = Bytes.wrap(to.getBytes());
   ```
   Please also check other occurrences of this additional space.

##########
File path: 
streams/src/test/java/org/apache/kafka/streams/state/internals/RocksDBRangeIteratorTest.java
##########
@@ -0,0 +1,419 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.kafka.streams.state.internals;
+
+import org.apache.kafka.common.utils.Bytes;
+import org.junit.Test;
+import org.rocksdb.RocksIterator;
+
+import java.util.Collections;
+import java.util.NoSuchElementException;
+
+import static org.easymock.EasyMock.mock;
+import static org.easymock.EasyMock.expect;
+import static org.easymock.EasyMock.expectLastCall;
+import static org.easymock.EasyMock.replay;
+import static org.easymock.EasyMock.verify;
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.core.Is.is;
+import static org.junit.Assert.assertThrows;
+
+public class RocksDBRangeIteratorTest {
+
+    private final String storeName = "store";
+    private final String key1 = "a";
+    private final String key2 = "b";
+    private final String key3 = "c";
+    private final String key4 = "d";
+
+    private final String value = "value";
+    private final  Bytes key1Bytes = Bytes.wrap(key1.getBytes());
+    private final  Bytes key2Bytes = Bytes.wrap(key2.getBytes());
+    private final  Bytes key3Bytes = Bytes.wrap(key3.getBytes());
+    private final  Bytes key4Bytes = Bytes.wrap(key4.getBytes());
+    private final byte[] valueBytes = value.getBytes();
+
+    @Test
+    public void shouldReturnAllKeysInTheRangeInForwardDirection() {
+
+        final RocksIterator rocksIterator = mock(RocksIterator.class);
+        rocksIterator.seek(key1Bytes.get());
+        expect(rocksIterator.isValid())
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(false);
+        expect(rocksIterator.key())
+            .andReturn(key1Bytes.get())
+            .andReturn(key2Bytes.get())
+            .andReturn(key3Bytes.get());
+        expect(rocksIterator.value()).andReturn(valueBytes).times(3);
+        rocksIterator.next();
+        expectLastCall().times(3);
+        replay(rocksIterator);
+        final RocksDBRangeIterator rocksDBRangeIterator = new 
RocksDBRangeIterator(
+                storeName,
+            rocksIterator,
+            Collections.emptySet(),
+            key1Bytes,
+            key3Bytes,
+            true
+        );
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key1Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key2Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key3Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(false));
+        verify(rocksIterator);
+    }
+
+    @Test
+    public void shouldReturnAllKeysInTheRangeReverseDirection() {
+
+        final RocksIterator rocksIterator = mock(RocksIterator.class);
+        rocksIterator.seekForPrev(key3Bytes.get());
+        expect(rocksIterator.isValid())
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(false);
+        expect(rocksIterator.key())
+            .andReturn(key3Bytes.get())
+            .andReturn(key2Bytes.get())
+            .andReturn(key1Bytes.get());
+        expect(rocksIterator.value()).andReturn(valueBytes).times(3);
+        rocksIterator.prev();
+        expectLastCall().times(3);
+        replay(rocksIterator);
+        final RocksDBRangeIterator rocksDBRangeIterator = new 
RocksDBRangeIterator(
+                storeName,
+            rocksIterator,
+            Collections.emptySet(),
+            key1Bytes,
+            key3Bytes,
+            false
+        );
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key3Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key2Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key1Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(false));
+        verify(rocksIterator);
+    }
+
+    @Test
+    public void 
shouldReturnAllKeysWhenLastKeyIsGreaterThanLargestKeyInStateStoreInForwardDirection()
 {
+
+        final String to = "f";
+        final  Bytes toBytes = Bytes.wrap(to.getBytes());
+        final RocksIterator rocksIterator = mock(RocksIterator.class);
+        rocksIterator.seek(key1Bytes.get());
+        expect(rocksIterator.isValid())
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(false);
+        expect(rocksIterator.key())
+            .andReturn(key1Bytes.get())
+            .andReturn(key2Bytes.get())
+            .andReturn(key3Bytes.get())
+            .andReturn(key4Bytes.get());
+        expect(rocksIterator.value()).andReturn(valueBytes).times(4);
+        rocksIterator.next();
+        expectLastCall().times(4);
+        replay(rocksIterator);
+        final RocksDBRangeIterator rocksDBRangeIterator = new 
RocksDBRangeIterator(
+                storeName,
+            rocksIterator,
+            Collections.emptySet(),
+            key1Bytes,
+            toBytes,
+            true
+        );
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key1Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key2Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key3Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key4Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(false));
+        verify(rocksIterator);
+    }
+
+
+    @Test
+    public void 
shouldReturnAllKeysWhenLastKeyIsSmallerThanSmallestKeyInStateStoreInReverseDirection()
 {
+        final String to = "a";
+        final  Bytes toBytes = Bytes.wrap(to.getBytes());
+
+        final RocksIterator rocksIterator = mock(RocksIterator.class);
+        rocksIterator.seekForPrev(key4Bytes.get());
+        expect(rocksIterator.isValid())
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(false);
+        expect(rocksIterator.key())
+            .andReturn(key4Bytes.get())
+            .andReturn(key3Bytes.get())
+            .andReturn(key2Bytes.get())
+            .andReturn(key1Bytes.get());
+        expect(rocksIterator.value()).andReturn(valueBytes).times(4);
+        rocksIterator.prev();
+        expectLastCall().times(4);
+        replay(rocksIterator);
+        final RocksDBRangeIterator rocksDBRangeIterator = new 
RocksDBRangeIterator(
+                storeName,
+            rocksIterator,
+            Collections.emptySet(),
+            toBytes,
+            key4Bytes,
+            false
+        );
+
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key4Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key3Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key2Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key1Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(false));
+        verify(rocksIterator);
+    }
+
+
+    @Test
+    public void 
shouldReturnNoKeysWhenLastKeyIsSmallerThanSmallestKeyInStateStoreForwardDirection()
 {
+
+        // key range in state store: [c-f]
+
+        final RocksIterator rocksIterator = mock(RocksIterator.class);
+        rocksIterator.seek(key1Bytes.get());
+        expect(rocksIterator.isValid())
+            .andReturn(false);
+
+        replay(rocksIterator);
+        final RocksDBRangeIterator rocksDBRangeIterator = new 
RocksDBRangeIterator(
+                storeName,
+            rocksIterator,
+            Collections.emptySet(),
+            key1Bytes,
+            key2Bytes,
+            true
+        );
+        assertThat(rocksDBRangeIterator.hasNext(), is(false));
+        verify(rocksIterator);
+
+    }
+
+    @Test
+    public void 
shouldReturnNoKeysWhenLastKeyIsLargerThanLargestKeyInStateStoreReverseDirection()
 {
+
+        // key range in state store: [c-f]
+        final String from = "g";
+        final String to = "h";
+
+        final  Bytes fromBytes = Bytes.wrap(from.getBytes());
+        final  Bytes toBytes = Bytes.wrap(to.getBytes());
+        final RocksIterator rocksIterator = mock(RocksIterator.class);
+        rocksIterator.seekForPrev(toBytes.get());
+        expect(rocksIterator.isValid())
+            .andReturn(false);
+
+        replay(rocksIterator);
+        final RocksDBRangeIterator rocksDBRangeIterator = new 
RocksDBRangeIterator(
+                storeName,
+            rocksIterator,
+            Collections.emptySet(),
+            fromBytes,
+            toBytes,
+            false
+        );
+        assertThat(rocksDBRangeIterator.hasNext(), is(false));
+        verify(rocksIterator);
+    }
+
+    @Test
+    public void 
shouldReturnAllKeysInPartiallyOverlappingRangeInForwardDirection() {
+
+        final RocksIterator rocksIterator = mock(RocksIterator.class);
+        rocksIterator.seek(key1Bytes.get());
+        expect(rocksIterator.isValid())
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(false);
+        expect(rocksIterator.key())
+            .andReturn(key2Bytes.get())
+            .andReturn(key3Bytes.get());
+        expect(rocksIterator.value()).andReturn(valueBytes).times(2);
+        rocksIterator.next();
+        expectLastCall().times(2);
+        replay(rocksIterator);
+        final RocksDBRangeIterator rocksDBRangeIterator = new 
RocksDBRangeIterator(
+                storeName,
+            rocksIterator,
+            Collections.emptySet(),
+            key1Bytes,
+            key3Bytes,
+            true
+        );
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key2Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key3Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(false));
+        verify(rocksIterator);
+    }
+
+    @Test
+    public void 
shouldReturnAllKeysInPartiallyOverlappingRangeInReverseDirection() {
+
+        final RocksIterator rocksIterator = mock(RocksIterator.class);
+        final String to = "e";
+        final Bytes toBytes = Bytes.wrap(to.getBytes());
+        rocksIterator.seekForPrev(toBytes.get());
+        expect(rocksIterator.isValid())
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(false);
+        expect(rocksIterator.key())
+            .andReturn(key4Bytes.get())
+            .andReturn(key3Bytes.get());
+        expect(rocksIterator.value()).andReturn(valueBytes).times(2);
+        rocksIterator.prev();
+        expectLastCall().times(2);
+        replay(rocksIterator);
+        final RocksDBRangeIterator rocksDBRangeIterator = new 
RocksDBRangeIterator(
+                storeName,
+            rocksIterator,
+            Collections.emptySet(),
+            key3Bytes,
+            toBytes,
+            false
+        );
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key4Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key3Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(false));
+        verify(rocksIterator);
+    }
+
+    @Test
+    public void 
shouldReturnTheCurrentKeyOnInvokingPeekNextKeyInForwardDirection() {
+        final RocksIterator rocksIterator = mock(RocksIterator.class);
+        rocksIterator.seek(key1Bytes.get());
+        expect(rocksIterator.isValid())
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(false);
+        expect(rocksIterator.key())
+            .andReturn(key2Bytes.get())
+            .andReturn(key3Bytes.get());
+        expect(rocksIterator.value()).andReturn(valueBytes).times(2);
+        rocksIterator.next();
+        expectLastCall().times(2);
+        replay(rocksIterator);
+        final RocksDBRangeIterator rocksDBRangeIterator = new 
RocksDBRangeIterator(
+                storeName,
+            rocksIterator,
+            Collections.emptySet(),
+            key1Bytes,
+            key3Bytes,
+            true
+        );
+
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.peekNextKey(), is(key2Bytes));
+        assertThat(rocksDBRangeIterator.next().key, is(key2Bytes));

Review comment:
       I think, it would be good to verify that a second call to  
`peekNextKey()` right after the first call to `peekNextKey()` returns the same 
value, since this is the main difference between `next()` and `peekNextKey()`.  

##########
File path: 
streams/src/test/java/org/apache/kafka/streams/state/internals/RocksDBRangeIteratorTest.java
##########
@@ -0,0 +1,419 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.kafka.streams.state.internals;
+
+import org.apache.kafka.common.utils.Bytes;
+import org.junit.Test;
+import org.rocksdb.RocksIterator;
+
+import java.util.Collections;
+import java.util.NoSuchElementException;
+
+import static org.easymock.EasyMock.mock;
+import static org.easymock.EasyMock.expect;
+import static org.easymock.EasyMock.expectLastCall;
+import static org.easymock.EasyMock.replay;
+import static org.easymock.EasyMock.verify;
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.core.Is.is;
+import static org.junit.Assert.assertThrows;
+
+public class RocksDBRangeIteratorTest {
+
+    private final String storeName = "store";
+    private final String key1 = "a";
+    private final String key2 = "b";
+    private final String key3 = "c";
+    private final String key4 = "d";
+
+    private final String value = "value";
+    private final  Bytes key1Bytes = Bytes.wrap(key1.getBytes());
+    private final  Bytes key2Bytes = Bytes.wrap(key2.getBytes());
+    private final  Bytes key3Bytes = Bytes.wrap(key3.getBytes());
+    private final  Bytes key4Bytes = Bytes.wrap(key4.getBytes());
+    private final byte[] valueBytes = value.getBytes();
+
+    @Test
+    public void shouldReturnAllKeysInTheRangeInForwardDirection() {
+
+        final RocksIterator rocksIterator = mock(RocksIterator.class);
+        rocksIterator.seek(key1Bytes.get());
+        expect(rocksIterator.isValid())
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(false);
+        expect(rocksIterator.key())
+            .andReturn(key1Bytes.get())
+            .andReturn(key2Bytes.get())
+            .andReturn(key3Bytes.get());
+        expect(rocksIterator.value()).andReturn(valueBytes).times(3);
+        rocksIterator.next();
+        expectLastCall().times(3);
+        replay(rocksIterator);
+        final RocksDBRangeIterator rocksDBRangeIterator = new 
RocksDBRangeIterator(
+                storeName,
+            rocksIterator,
+            Collections.emptySet(),
+            key1Bytes,
+            key3Bytes,
+            true
+        );
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key1Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key2Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key3Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(false));
+        verify(rocksIterator);
+    }
+
+    @Test
+    public void shouldReturnAllKeysInTheRangeReverseDirection() {
+
+        final RocksIterator rocksIterator = mock(RocksIterator.class);
+        rocksIterator.seekForPrev(key3Bytes.get());
+        expect(rocksIterator.isValid())
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(true)
+            .andReturn(false);
+        expect(rocksIterator.key())
+            .andReturn(key3Bytes.get())
+            .andReturn(key2Bytes.get())
+            .andReturn(key1Bytes.get());
+        expect(rocksIterator.value()).andReturn(valueBytes).times(3);
+        rocksIterator.prev();
+        expectLastCall().times(3);
+        replay(rocksIterator);
+        final RocksDBRangeIterator rocksDBRangeIterator = new 
RocksDBRangeIterator(
+                storeName,
+            rocksIterator,
+            Collections.emptySet(),
+            key1Bytes,
+            key3Bytes,
+            false
+        );
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key3Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key2Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(true));
+        assertThat(rocksDBRangeIterator.next().key, is(key1Bytes));
+        assertThat(rocksDBRangeIterator.hasNext(), is(false));
+        verify(rocksIterator);
+    }
+
+    @Test
+    public void 
shouldReturnAllKeysWhenLastKeyIsGreaterThanLargestKeyInStateStoreInForwardDirection()
 {
+
+        final String to = "f";

Review comment:
       nit: Couldn't you Instead of using a literal, use 
`Bytes.increment(key4Bytes)` for the `to` parameter?  

##########
File path: 
streams/src/test/java/org/apache/kafka/streams/state/internals/RocksDBRangeIteratorTest.java
##########
@@ -0,0 +1,419 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.kafka.streams.state.internals;
+
+import org.apache.kafka.common.utils.Bytes;
+import org.junit.Test;
+import org.rocksdb.RocksIterator;
+
+import java.util.Collections;
+import java.util.NoSuchElementException;
+
+import static org.easymock.EasyMock.mock;
+import static org.easymock.EasyMock.expect;
+import static org.easymock.EasyMock.expectLastCall;
+import static org.easymock.EasyMock.replay;
+import static org.easymock.EasyMock.verify;
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.core.Is.is;
+import static org.junit.Assert.assertThrows;
+
+public class RocksDBRangeIteratorTest {
+
+    private final String storeName = "store";
+    private final String key1 = "a";
+    private final String key2 = "b";
+    private final String key3 = "c";
+    private final String key4 = "d";
+
+    private final String value = "value";
+    private final  Bytes key1Bytes = Bytes.wrap(key1.getBytes());
+    private final  Bytes key2Bytes = Bytes.wrap(key2.getBytes());
+    private final  Bytes key3Bytes = Bytes.wrap(key3.getBytes());
+    private final  Bytes key4Bytes = Bytes.wrap(key4.getBytes());
+    private final byte[] valueBytes = value.getBytes();
+
+    @Test
+    public void shouldReturnAllKeysInTheRangeInForwardDirection() {
+

Review comment:
       Please remove empty lines here and in the other test methods.




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