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   * 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.
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  package org.apache.kafka.clients.producer;
  
  import org.apache.kafka.common.Cluster;
  import org.apache.kafka.common.Node;
  import org.apache.kafka.common.PartitionInfo;
  
  import org.junit.jupiter.api.Test;
  
  import java.util.Collections;
  import java.util.HashMap;
  import java.util.List;
  import java.util.Map;
  
  import static java.util.Arrays.asList;
  import static org.junit.jupiter.api.Assertions.assertEquals;
  import static org.junit.jupiter.api.Assertions.assertTrue;
  
  public class RoundRobinPartitionerTest {
      private static final Node[] NODES = new Node[] {
          new Node(0, "localhost", 99),
          new Node(1, "localhost", 100),
          new Node(2, "localhost", 101)
      };
  
      @Test
      public void testRoundRobinWithUnavailablePartitions() {
          // Intentionally make the partition list not in partition order to test the edge
          // cases.
          List<PartitionInfo> partitions = asList(
                  new PartitionInfo("test", 1, null, NODES, NODES),
                  new PartitionInfo("test", 2, NODES[1], NODES, NODES),
                  new PartitionInfo("test", 0, NODES[0], NODES, NODES));
          // When there are some unavailable partitions, we want to make sure that (1) we
          // always pick an available partition,
          // and (2) the available partitions are selected in a round robin way.
          int countForPart0 = 0;
          int countForPart2 = 0;
          Partitioner partitioner = new RoundRobinPartitioner();
          Cluster cluster = new Cluster("clusterId", asList(NODES[0], NODES[1], NODES[2]), partitions,
              Collections.emptySet(), Collections.emptySet());
          for (int i = 1; i <= 100; i++) {
              int part = partitioner.partition("test", null, null, null, null, cluster);
              assertTrue(part == 0 || part == 2, "We should never choose a leader-less node in round robin");
              if (part == 0)
                  countForPart0++;
              else
                  countForPart2++;
          }
          assertEquals(countForPart0, countForPart2, "The distribution between two available partitions should be even");
      }
  
      @Test
      public void testRoundRobinWithKeyBytes() {
          final String topicA = "topicA";
          final String topicB = "topicB";
  
          List<PartitionInfo> allPartitions = asList(new PartitionInfo(topicA, 0, NODES[0], NODES, NODES),
                  new PartitionInfo(topicA, 1, NODES[1], NODES, NODES), new PartitionInfo(topicA, 2, NODES[2], NODES, NODES),
                  new PartitionInfo(topicB, 0, NODES[0], NODES, NODES));
          Cluster testCluster = new Cluster("clusterId", asList(NODES[0], NODES[1], NODES[2]), allPartitions,
                  Collections.emptySet(), Collections.emptySet());
  
          final Map<Integer, Integer> partitionCount = new HashMap<>();
  
          final byte[] keyBytes = "key".getBytes();
          Partitioner partitioner = new RoundRobinPartitioner();
          for (int i = 0; i < 30; ++i) {
              int partition = partitioner.partition(topicA, null, keyBytes, null, null, testCluster);
              Integer count = partitionCount.get(partition);
              if (null == count)
                  count = 0;
              partitionCount.put(partition, count + 1);
  
              if (i % 5 == 0) {
                  partitioner.partition(topicB, null, keyBytes, null, null, testCluster);
              }
          }
  
          assertEquals(10, partitionCount.get(0).intValue());
          assertEquals(10, partitionCount.get(1).intValue());
          assertEquals(10, partitionCount.get(2).intValue());
      }
  }
  