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.common.utils;
  
  import org.junit.jupiter.api.Test;
  
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.Collections;
  import java.util.List;
  import java.util.stream.Collectors;
  
  import static java.util.Arrays.asList;
  import static java.util.Collections.emptyList;
  import static org.junit.jupiter.api.Assertions.assertEquals;
  
  public class FlattenedIteratorTest {
  
      @Test
      public void testNestedLists() {
          List<List<String>> list = asList(
              asList("foo", "a", "bc"),
              Collections.singletonList("ddddd"),
              asList("", "bar2", "baz45"));
  
          Iterable<String> flattenedIterable = () -> new FlattenedIterator<>(list.iterator(), List::iterator);
          List<String> flattened = new ArrayList<>();
          flattenedIterable.forEach(flattened::add);
  
          assertEquals(list.stream().flatMap(Collection::stream).collect(Collectors.toList()), flattened);
  
          // Ensure we can iterate multiple times
          List<String> flattened2 = new ArrayList<>();
          flattenedIterable.forEach(flattened2::add);
  
          assertEquals(flattened, flattened2);
      }
  
      @Test
      public void testEmptyList() {
          List<List<String>> list = emptyList();
  
          Iterable<String> flattenedIterable = () -> new FlattenedIterator<>(list.iterator(), List::iterator);
          List<String> flattened = new ArrayList<>();
          flattenedIterable.forEach(flattened::add);
  
          assertEquals(emptyList(), flattened);
      }
  
      @Test
      public void testNestedSingleEmptyList() {
          List<List<String>> list = Collections.singletonList(emptyList());
  
          Iterable<String> flattenedIterable = () -> new FlattenedIterator<>(list.iterator(), List::iterator);
          List<String> flattened = new ArrayList<>();
          flattenedIterable.forEach(flattened::add);
  
          assertEquals(emptyList(), flattened);
      }
  
      @Test
      public void testEmptyListFollowedByNonEmpty() {
          List<List<String>> list = asList(
              emptyList(),
              asList("boo", "b", "de"));
  
          Iterable<String> flattenedIterable = () -> new FlattenedIterator<>(list.iterator(), List::iterator);
          List<String> flattened = new ArrayList<>();
          flattenedIterable.forEach(flattened::add);
  
          assertEquals(list.stream().flatMap(Collection::stream).collect(Collectors.toList()), flattened);
      }
  
      @Test
      public void testEmptyListInBetweenNonEmpty() {
          List<List<String>> list = asList(
              Collections.singletonList("aadwdwdw"),
              emptyList(),
              asList("ee", "aa", "dd"));
  
          Iterable<String> flattenedIterable = () -> new FlattenedIterator<>(list.iterator(), List::iterator);
          List<String> flattened = new ArrayList<>();
          flattenedIterable.forEach(flattened::add);
  
          assertEquals(list.stream().flatMap(Collection::stream).collect(Collectors.toList()), flattened);
      }
  
      @Test
      public void testEmptyListAtTheEnd() {
          List<List<String>> list = asList(
              asList("ee", "dd"),
              Collections.singletonList("e"),
              emptyList());
  
          Iterable<String> flattenedIterable = () -> new FlattenedIterator<>(list.iterator(), List::iterator);
          List<String> flattened = new ArrayList<>();
          flattenedIterable.forEach(flattened::add);
  
          assertEquals(list.stream().flatMap(Collection::stream).collect(Collectors.toList()), flattened);
      }
  
  }
  