content: /*
   * 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.kstream.internals;
  
  import org.apache.kafka.common.serialization.IntegerSerializer;
  import org.apache.kafka.common.serialization.Serdes;
  import org.apache.kafka.common.serialization.StringSerializer;
  import org.apache.kafka.streams.KeyValue;
  import org.apache.kafka.streams.StreamsBuilder;
  import org.apache.kafka.streams.TestInputTopic;
  import org.apache.kafka.streams.TopologyTestDriver;
  import org.apache.kafka.streams.kstream.Consumed;
  import org.apache.kafka.streams.kstream.ForeachAction;
  import org.apache.kafka.streams.kstream.KStream;
  import org.apache.kafka.test.StreamsTestUtils;
  
  import org.junit.jupiter.api.Test;
  
  import java.util.ArrayList;
  import java.util.List;
  import java.util.Properties;
  
  import static org.junit.jupiter.api.Assertions.assertEquals;
  import static org.junit.jupiter.api.Assertions.fail;
  
  public class KStreamPeekTest {
  
      private final String topicName = "topic";
      private final Properties props = StreamsTestUtils.getStreamsConfig(Serdes.Integer(), Serdes.String());
  
      @Test
      public void shouldObserveStreamElements() {
          final StreamsBuilder builder = new StreamsBuilder();
          final KStream<Integer, String> stream = builder.stream(topicName, Consumed.with(Serdes.Integer(), Serdes.String()));
          final List<KeyValue<Integer, String>> peekObserved = new ArrayList<>(), streamObserved = new ArrayList<>();
          stream.peek(collect(peekObserved)).foreach(collect(streamObserved));
  
          try (final TopologyTestDriver driver = new TopologyTestDriver(builder.build(), props)) {
              final TestInputTopic<Integer, String> inputTopic = driver.createInputTopic(topicName, new IntegerSerializer(), new StringSerializer());
              final List<KeyValue<Integer, String>> expected = new ArrayList<>();
              for (int key = 0; key < 32; key++) {
                  final String value = "V" + key;
                  inputTopic.pipeInput(key, value);
                  expected.add(new KeyValue<>(key, value));
              }
  
              assertEquals(expected, peekObserved);
              assertEquals(expected, streamObserved);
          }
      }
  
      @Test
      public void shouldNotAllowNullAction() {
          final StreamsBuilder builder = new StreamsBuilder();
          final KStream<Integer, String> stream = builder.stream(topicName, Consumed.with(Serdes.Integer(), Serdes.String()));
          try {
              stream.peek(null);
              fail("expected null action to throw NPE");
          } catch (final NullPointerException expected) {
              // do nothing
          }
      }
  
      private static <K, V> ForeachAction<K, V> collect(final List<KeyValue<K, V>> into) {
          return (key, value) -> into.add(new KeyValue<>(key, value));
      }
  }
  