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.KeyValueTimestamp;
  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.KStream;
  import org.apache.kafka.streams.kstream.KeyValueMapper;
  import org.apache.kafka.streams.processor.api.Record;
  import org.apache.kafka.test.MockApiProcessorSupplier;
  import org.apache.kafka.test.StreamsTestUtils;
  
  import org.junit.jupiter.api.Test;
  
  import java.time.Duration;
  import java.time.Instant;
  import java.util.ArrayList;
  import java.util.Properties;
  
  import static org.hamcrest.MatcherAssert.assertThat;
  import static org.hamcrest.core.Is.is;
  import static org.junit.jupiter.api.Assertions.assertEquals;
  import static org.junit.jupiter.api.Assertions.assertThrows;
  
  public class KStreamFlatMapTest {
      private final Properties props = StreamsTestUtils.getStreamsConfig(Serdes.Integer(), Serdes.String());
  
      @Test
      public void testFlatMap() {
          final StreamsBuilder builder = new StreamsBuilder();
          final String topicName = "topic";
  
          final KeyValueMapper<Number, Object, Iterable<KeyValue<String, String>>> mapper =
              (key, value) -> {
                  final ArrayList<KeyValue<String, String>> result = new ArrayList<>();
                  for (int i = 0; i < key.intValue(); i++) {
                      result.add(KeyValue.pair(Integer.toString(key.intValue() * 10 + i), value.toString()));
                  }
                  return result;
              };
  
          final int[] expectedKeys = {0, 1, 2, 3};
  
          final KStream<Integer, String> stream;
          final MockApiProcessorSupplier<String, String, Void, Void> supplier = new MockApiProcessorSupplier<>();
          stream = builder.stream(topicName, Consumed.with(Serdes.Integer(), Serdes.String()));
          stream.flatMap(mapper).process(supplier);
  
          try (final TopologyTestDriver driver = new TopologyTestDriver(builder.build(), props)) {
              final TestInputTopic<Integer, String> inputTopic =
                      driver.createInputTopic(topicName, new IntegerSerializer(), new StringSerializer(), Instant.ofEpochMilli(0), Duration.ZERO);
              for (final int expectedKey : expectedKeys) {
                  inputTopic.pipeInput(expectedKey, "V" + expectedKey);
              }
          }
  
          assertEquals(6, supplier.theCapturedProcessor().processed().size());
  
          final KeyValueTimestamp[] expected = {new KeyValueTimestamp<>("10", "V1", 0),
              new KeyValueTimestamp<>("20", "V2", 0),
              new KeyValueTimestamp<>("21", "V2", 0),
              new KeyValueTimestamp<>("30", "V3", 0),
              new KeyValueTimestamp<>("31", "V3", 0),
              new KeyValueTimestamp<>("32", "V3", 0)};
  
          for (int i = 0; i < expected.length; i++) {
              assertEquals(expected[i], supplier.theCapturedProcessor().processed().get(i));
          }
      }
  
      @Test
      public void testKeyValueMapperResultNotNull() {
          final KStreamFlatMap<String, Integer, String, Integer> supplier = new KStreamFlatMap<>((key, value) -> null);
          final Throwable throwable = assertThrows(NullPointerException.class,
                  () -> supplier.get().process(new Record<>("K", 0, 0L)));
          assertThat(throwable.getMessage(), is("The provided KeyValueMapper returned null which is not allowed."));
      }
  }
  