code: /*
   * Copyright (c) 2016-present, RxJava Contributors.
   *
   * Licensed 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 io.reactivex.rxjava3.internal.operators.flowable;
  
  import java.util.concurrent.atomic.AtomicBoolean;
  
  import org.junit.*;
  
  import io.reactivex.rxjava3.core.*;
  import io.reactivex.rxjava3.functions.Action;
  import io.reactivex.rxjava3.subscribers.TestSubscriber;
  
  public class FlowableToSingleTest extends RxJavaTest {
  
      @Test
      public void justSingleItemObservable() {
          TestSubscriber<String> subscriber = TestSubscriber.create();
          Single<String> single = Flowable.just("Hello World!").single("");
          single.toFlowable().subscribe(subscriber);
  
          subscriber.assertResult("Hello World!");
      }
  
      @Test
      public void errorObservable() {
          TestSubscriber<String> subscriber = TestSubscriber.create();
          IllegalArgumentException error = new IllegalArgumentException("Error");
          Single<String> single = Flowable.<String>error(error).single("");
          single.toFlowable().subscribe(subscriber);
  
          subscriber.assertError(error);
      }
  
      @Test
      public void justTwoEmissionsObservableThrowsError() {
          TestSubscriber<String> subscriber = TestSubscriber.create();
          Single<String> single = Flowable.just("First", "Second").single("");
          single.toFlowable().subscribe(subscriber);
  
          subscriber.assertError(IllegalArgumentException.class);
      }
  
      @Test
      public void emptyObservable() {
          TestSubscriber<String> subscriber = TestSubscriber.create();
          Single<String> single = Flowable.<String>empty().single("");
          single.toFlowable().subscribe(subscriber);
  
          subscriber.assertResult("");
      }
  
      @Test
      public void repeatObservableThrowsError() {
          TestSubscriber<String> subscriber = TestSubscriber.create();
          Single<String> single = Flowable.just("First", "Second").repeat().single("");
          single.toFlowable().subscribe(subscriber);
  
          subscriber.assertError(IllegalArgumentException.class);
      }
  
      @Test
      public void shouldUseUnsafeSubscribeInternallyNotSubscribe() {
          TestSubscriber<String> subscriber = TestSubscriber.create();
          final AtomicBoolean unsubscribed = new AtomicBoolean(false);
          Single<String> single = Flowable.just("Hello World!").doOnCancel(new Action() {
  
              @Override
              public void run() {
                  unsubscribed.set(true);
              }}).single("");
          single.toFlowable().subscribe(subscriber);
          subscriber.assertComplete();
          Assert.assertFalse(unsubscribed.get());
      }
  }
  