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.observable;
  
  import static org.junit.Assert.*;
  import static org.mockito.ArgumentMatchers.*;
  import static org.mockito.Mockito.*;
  
  import java.util.NoSuchElementException;
  import java.util.concurrent.atomic.AtomicReference;
  
  import org.junit.Test;
  import org.mockito.InOrder;
  
  import io.reactivex.rxjava3.core.*;
  import io.reactivex.rxjava3.functions.*;
  import io.reactivex.rxjava3.plugins.RxJavaPlugins;
  import io.reactivex.rxjava3.testsupport.TestHelper;
  
  public class ObservableSingleTest extends RxJavaTest {
  
      @Test
      public void singleObservable() {
          Observable<Integer> o = Observable.just(1).singleElement().toObservable();
  
          Observer<Integer> observer = TestHelper.mockObserver();
          o.subscribe(observer);
  
          InOrder inOrder = inOrder(observer);
          inOrder.verify(observer, times(1)).onNext(1);
          inOrder.verify(observer, times(1)).onComplete();
          inOrder.verifyNoMoreInteractions();
      }
  
      @Test
      public void singleWithTooManyElementsObservable() {
          Observable<Integer> o = Observable.just(1, 2).singleElement().toObservable();
  
          Observer<Integer> observer = TestHelper.mockObserver();
          o.subscribe(observer);
  
          InOrder inOrder = inOrder(observer);
          inOrder.verify(observer, times(1)).onError(
                  isA(IllegalArgumentException.class));
          inOrder.verifyNoMoreInteractions();
      }
  
      @Test
      public void singleWithEmptyObservable() {
          Observable<Integer> o = Observable.<Integer> empty().singleElement().toObservable();
  
          Observer<Integer> observer = TestHelper.mockObserver();
          o.subscribe(observer);
  
          InOrder inOrder = inOrder(observer);
          inOrder.verify(observer).onComplete();
          inOrder.verify(observer, never()).onError(any(Throwable.class));
          inOrder.verifyNoMoreInteractions();
      }
  
      @Test
      public void singleWithPredicateObservable() {
          Observable<Integer> o = Observable.just(1, 2)
                  .filter(
                  new Predicate<Integer>() {
  
                      @Override
                      public boolean test(Integer t1) {
                          return t1 % 2 == 0;
                      }
                  })
                  .singleElement().toObservable();
  
          Observer<Integer> observer = TestHelper.mockObserver();
          o.subscribe(observer);
  
          InOrder inOrder = inOrder(observer);
          inOrder.verify(observer, times(1)).onNext(2);
          inOrder.verify(observer, times(1)).onComplete();
          inOrder.verifyNoMoreInteractions();
      }
  
      @Test
      public void singleWithPredicateAndTooManyElementsObservable() {
          Observable<Integer> o = Observable.just(1, 2, 3, 4)
                  .filter(
                  new Predicate<Integer>() {
  
                      @Override
                      public boolean test(Integer t1) {
                          return t1 % 2 == 0;
                      }
                  })
                  .singleElement().toObservable();
  
          Observer<Integer> observer = TestHelper.mockObserver();
          o.subscribe(observer);
  
          InOrder inOrder = inOrder(observer);
          inOrder.verify(observer, times(1)).onError(
                  isA(IllegalArgumentException.class));
          inOrder.verifyNoMoreInteractions();
      }
  
      @Test
      public void singleWithPredicateAndEmptyObservable() {
          Observable<Integer> o = Observable.just(1)
                  .filter(
                  new Predicate<Integer>() {
  
                      @Override
                      public boolean test(Integer t1) {
                          return t1 % 2 == 0;
                      }
                  })
                  .singleElement().toObservable();
          Observer<Integer> observer = TestHelper.mockObserver();
          o.subscribe(observer);
  
          InOrder inOrder = inOrder(observer);
          inOrder.verify(observer).onComplete();
          inOrder.verify(observer, never()).onError(any(Throwable.class));
          inOrder.verifyNoMoreInteractions();
      }
  
      @Test
      public void singleOrDefaultObservable() {
          Observable<Integer> o = Observable.just(1).single(2).toObservable();
  
          Observer<Integer> observer = TestHelper.mockObserver();
          o.subscribe(observer);
  
          InOrder inOrder = inOrder(observer);
          inOrder.verify(observer, times(1)).onNext(1);
          inOrder.verify(observer, times(1)).onComplete();
          inOrder.verifyNoMoreInteractions();
      }
  
      @Test
      public void singleOrDefaultWithTooManyElementsObservable() {
          Observable<Integer> o = Observable.just(1, 2).single(3).toObservable();
  
          Observer<Integer> observer = TestHelper.mockObserver();
          o.subscribe(observer);
  
          InOrder inOrder = inOrder(observer);
          inOrder.verify(observer, times(1)).onError(
                  isA(IllegalArgumentException.class));
          inOrder.verifyNoMoreInteractions();
      }
  
      @Test
      public void singleOrDefaultWithEmptyObservable() {
          Observable<Integer> o = Observable.<Integer> empty()
                  .single(1).toObservable();
  
          Observer<Integer> observer = TestHelper.mockObserver();
          o.subscribe(observer);
  
          InOrder inOrder = inOrder(observer);
          inOrder.verify(observer, times(1)).onNext(1);
          inOrder.verify(observer, times(1)).onComplete();
          inOrder.verifyNoMoreInteractions();
      }
  
      @Test
      public void singleOrDefaultWithPredicateObservable() {
          Observable<Integer> o = Observable.just(1, 2)
                  .filter(new Predicate<Integer>() {
                      @Override
                      public boolean test(Integer t1) {
                          return t1 % 2 == 0;
                      }
                  })
                  .single(4).toObservable();
  
          Observer<Integer> observer = TestHelper.mockObserver();
          o.subscribe(observer);
  
          InOrder inOrder = inOrder(observer);
          inOrder.verify(observer, times(1)).onNext(2);
          inOrder.verify(observer, times(1)).onComplete();
          inOrder.verifyNoMoreInteractions();
      }
  
      @Test
      public void singleOrDefaultWithPredicateAndTooManyElementsObservable() {
          Observable<Integer> o = Observable.just(1, 2, 3, 4)
                  .filter(new Predicate<Integer>() {
                      @Override
                      public boolean test(Integer t1) {
                          return t1 % 2 == 0;
                      }
                  })
                  .single(6).toObservable();
  
          Observer<Integer> observer = TestHelper.mockObserver();
          o.subscribe(observer);
  
          InOrder inOrder = inOrder(observer);
          inOrder.verify(observer, times(1)).onError(
                  isA(IllegalArgumentException.class));
          inOrder.verifyNoMoreInteractions();
      }
  
      @Test
      public void singleOrDefaultWithPredicateAndEmptyObservable() {
          Observable<Integer> o = Observable.just(1)
                  .filter(new Predicate<Integer>() {
                      @Override
                      public boolean test(Integer t1) {
                          return t1 % 2 == 0;
                      }
                  })
                  .single(2).toObservable();
  
          Observer<Integer> observer = TestHelper.mockObserver();
          o.subscribe(observer);
  
          InOrder inOrder = inOrder(observer);
          inOrder.verify(observer, times(1)).onNext(2);
          inOrder.verify(observer, times(1)).onComplete();
          inOrder.verifyNoMoreInteractions();
      }
  
      @Test
      public void issue1527Observable() throws InterruptedException {
          //https://github.com/ReactiveX/RxJava/pull/1527
          Observable<Integer> source = Observable.just(1, 2, 3, 4, 5, 6);
          Observable<Integer> reduced = source.reduce(new BiFunction<Integer, Integer, Integer>() {
              @Override
              public Integer apply(Integer i1, Integer i2) {
                  return i1 + i2;
              }
          }).toObservable();
  
          Integer r = reduced.blockingFirst();
          assertEquals(21, r.intValue());
      }
  
      @Test
      public void single() {
          Maybe<Integer> o = Observable.just(1).singleElement();
  
          MaybeObserver<Integer> observer = TestHelper.mockMaybeObserver();
          o.subscribe(observer);
  
          InOrder inOrder = inOrder(observer);
          inOrder.verify(observer, times(1)).onSuccess(1);
          inOrder.verifyNoMoreInteractions();
      }
  
      @Test
      public void singleWithTooManyElements() {
          Maybe<Integer> o = Observable.just(1, 2).singleElement();
  
          MaybeObserver<Integer> observer = TestHelper.mockMaybeObserver();
          o.subscribe(observer);
  
          InOrder inOrder = inOrder(observer);
          inOrder.verify(observer, times(1)).onError(
                  isA(IllegalArgumentException.class));
          inOrder.verifyNoMoreInteractions();
      }
  
      @Test
      public void singleWithEmpty() {
          Maybe<Integer> o = Observable.<Integer> empty().singleElement();
  
          MaybeObserver<Integer> observer = TestHelper.mockMaybeObserver();
          o.subscribe(observer);
  
          InOrder inOrder = inOrder(observer);
          inOrder.verify(observer).onComplete();
          inOrder.verify(observer, never()).onError(any(Throwable.class));
          inOrder.verifyNoMoreInteractions();
      }
  
      @Test
      public void singleWithPredicate() {
          Maybe<Integer> o = Observable.just(1, 2)
                  .filter(
                  new Predicate<Integer>() {
  
                      @Override
                      public boolean test(Integer t1) {
                          return t1 % 2 == 0;
                      }
                  })
                  .singleElement();
  
          MaybeObserver<Integer> observer = TestHelper.mockMaybeObserver();
          o.subscribe(observer);
  
          InOrder inOrder = inOrder(observer);
          inOrder.verify(observer, times(1)).onSuccess(2);
          inOrder.verifyNoMoreInteractions();
      }
  
      @Test
      public void singleWithPredicateAndTooManyElements() {
          Maybe<Integer> o = Observable.just(1, 2, 3, 4)
                  .filter(
                  new Predicate<Integer>() {
  
                      @Override
                      public boolean test(Integer t1) {
                          return t1 % 2 == 0;
                      }
                  })
                  .singleElement();
  
          MaybeObserver<Integer> observer = TestHelper.mockMaybeObserver();
          o.subscribe(observer);
  
          InOrder inOrder = inOrder(observer);
          inOrder.verify(observer, times(1)).onError(
                  isA(IllegalArgumentException.class));
          inOrder.verifyNoMoreInteractions();
      }
  
      @Test
      public void singleWithPredicateAndEmpty() {
          Maybe<Integer> o = Observable.just(1)
                  .filter(
                  new Predicate<Integer>() {
  
                      @Override
                      public boolean test(Integer t1) {
                          return t1 % 2 == 0;
                      }
                  })
                  .singleElement();
          MaybeObserver<Integer> observer = TestHelper.mockMaybeObserver();
          o.subscribe(observer);
  
          InOrder inOrder = inOrder(observer);
          inOrder.verify(observer).onComplete();
          inOrder.verify(observer, never()).onError(any(Throwable.class));
          inOrder.verifyNoMoreInteractions();
      }
  
      @Test
      public void singleOrDefault() {
          Single<Integer> o = Observable.just(1).single(2);
  
          SingleObserver<Integer> observer = TestHelper.mockSingleObserver();
          o.subscribe(observer);
  
          InOrder inOrder = inOrder(observer);
          inOrder.verify(observer, times(1)).onSuccess(1);
          inOrder.verifyNoMoreInteractions();
      }
  
      @Test
      public void singleOrDefaultWithTooManyElements() {
          Single<Integer> o = Observable.just(1, 2).single(3);
  
          SingleObserver<Integer> observer = TestHelper.mockSingleObserver();
          o.subscribe(observer);
  
          InOrder inOrder = inOrder(observer);
          inOrder.verify(observer, times(1)).onError(
                  isA(IllegalArgumentException.class));
          inOrder.verifyNoMoreInteractions();
      }
  
      @Test
      public void singleOrDefaultWithEmpty() {
          Single<Integer> o = Observable.<Integer> empty()
                  .single(1);
  
          SingleObserver<Integer> observer = TestHelper.mockSingleObserver();
          o.subscribe(observer);
  
          InOrder inOrder = inOrder(observer);
          inOrder.verify(observer, times(1)).onSuccess(1);
          inOrder.verifyNoMoreInteractions();
      }
  
      @Test
      public void singleOrDefaultWithPredicate() {
          Single<Integer> o = Observable.just(1, 2)
                  .filter(new Predicate<Integer>() {
                      @Override
                      public boolean test(Integer t1) {
                          return t1 % 2 == 0;
                      }
                  })
                  .single(4);
  
          SingleObserver<Integer> observer = TestHelper.mockSingleObserver();
          o.subscribe(observer);
  
          InOrder inOrder = inOrder(observer);
          inOrder.verify(observer, times(1)).onSuccess(2);
          inOrder.verifyNoMoreInteractions();
      }
  
      @Test
      public void singleOrDefaultWithPredicateAndTooManyElements() {
          Single<Integer> o = Observable.just(1, 2, 3, 4)
                  .filter(new Predicate<Integer>() {
                      @Override
                      public boolean test(Integer t1) {
                          return t1 % 2 == 0;
                      }
                  })
                  .single(6);
  
          SingleObserver<Integer> observer = TestHelper.mockSingleObserver();
          o.subscribe(observer);
  
          InOrder inOrder = inOrder(observer);
          inOrder.verify(observer, times(1)).onError(
                  isA(IllegalArgumentException.class));
          inOrder.verifyNoMoreInteractions();
      }
  
      @Test
      public void singleOrDefaultWithPredicateAndEmpty() {
          Single<Integer> o = Observable.just(1)
                  .filter(new Predicate<Integer>() {
                      @Override
                      public boolean test(Integer t1) {
                          return t1 % 2 == 0;
                      }
                  })
                  .single(2);
  
          SingleObserver<Integer> observer = TestHelper.mockSingleObserver();
          o.subscribe(observer);
  
          InOrder inOrder = inOrder(observer);
          inOrder.verify(observer, times(1)).onSuccess(2);
          inOrder.verifyNoMoreInteractions();
      }
  
      @Test
      public void issue1527() throws InterruptedException {
          //https://github.com/ReactiveX/RxJava/pull/1527
          Observable<Integer> source = Observable.just(1, 2, 3, 4, 5, 6);
          Maybe<Integer> reduced = source.reduce(new BiFunction<Integer, Integer, Integer>() {
              @Override
              public Integer apply(Integer i1, Integer i2) {
                  return i1 + i2;
              }
          });
  
          Integer r = reduced.blockingGet();
          assertEquals(21, r.intValue());
      }
  
      @Test
      public void singleElementOperatorDoNotSwallowExceptionWhenDone() {
          final Throwable exception = new RuntimeException("some error");
          final AtomicReference<Throwable> error = new AtomicReference<>();
  
          try {
              RxJavaPlugins.setErrorHandler(new Consumer<Throwable>() {
                  @Override public void accept(final Throwable throwable) throws Exception {
                      error.set(throwable);
                  }
              });
  
              Observable.unsafeCreate(new ObservableSource<Integer>() {
                  @Override public void subscribe(final Observer<? super Integer> observer) {
                      observer.onComplete();
                      observer.onError(exception);
                  }
              }).singleElement().test().assertComplete();
  
              assertSame(exception, error.get().getCause());
          } finally {
              RxJavaPlugins.reset();
          }
      }
  
      @Test
      public void singleOrErrorNoElement() {
          Observable.empty()
              .singleOrError()
              .test()
              .assertNoValues()
              .assertError(NoSuchElementException.class);
      }
  
      @Test
      public void singleOrErrorOneElement() {
          Observable.just(1)
              .singleOrError()
              .test()
              .assertNoErrors()
              .assertValue(1);
      }
  
      @Test
      public void singleOrErrorMultipleElements() {
          Observable.just(1, 2, 3)
              .singleOrError()
              .test()
              .assertNoValues()
              .assertError(IllegalArgumentException.class);
      }
  
      @Test
      public void singleOrErrorError() {
          Observable.error(new RuntimeException("error"))
              .singleOrError()
              .to(TestHelper.testConsumer())
              .assertNoValues()
              .assertErrorMessage("error")
              .assertError(RuntimeException.class);
      }
  
      @Test
      public void badSource() {
          TestHelper.checkBadSourceObservable(new Function<Observable<Object>, Object>() {
              @Override
              public Object apply(Observable<Object> o) throws Exception {
                  return o.singleOrError();
              }
          }, false, 1, 1, 1);
  
          TestHelper.checkBadSourceObservable(new Function<Observable<Object>, Object>() {
              @Override
              public Object apply(Observable<Object> o) throws Exception {
                  return o.singleElement();
              }
          }, false, 1, 1, 1);
      }
  
      @Test
      public void doubleOnSubscribe() {
          TestHelper.checkDoubleOnSubscribeObservableToSingle(new Function<Observable<Object>, SingleSource<Object>>() {
              @Override
              public SingleSource<Object> apply(Observable<Object> o) throws Exception {
                  return o.singleOrError();
              }
          });
  
          TestHelper.checkDoubleOnSubscribeObservableToMaybe(new Function<Observable<Object>, MaybeSource<Object>>() {
              @Override
              public MaybeSource<Object> apply(Observable<Object> o) throws Exception {
                  return o.singleElement();
              }
          });
      }
  
      @Test
      public void singleOrError() {
          Observable.empty()
          .singleOrError()
          .toObservable()
          .test()
          .assertFailure(NoSuchElementException.class);
      }
  }
  