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.any;
  import static org.mockito.Mockito.*;
  
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.atomic.AtomicInteger;
  
  import org.junit.Test;
  import org.mockito.InOrder;
  
  import io.reactivex.rxjava3.core.*;
  import io.reactivex.rxjava3.exceptions.TestException;
  import io.reactivex.rxjava3.functions.*;
  import io.reactivex.rxjava3.observers.*;
  import io.reactivex.rxjava3.schedulers.Schedulers;
  import io.reactivex.rxjava3.testsupport.TestHelper;
  
  public class ObservableTakeLastTest extends RxJavaTest {
  
      @Test
      public void takeLastEmpty() {
          Observable<String> w = Observable.empty();
          Observable<String> take = w.takeLast(2);
  
          Observer<String> observer = TestHelper.mockObserver();
          take.subscribe(observer);
          verify(observer, never()).onNext(any(String.class));
          verify(observer, never()).onError(any(Throwable.class));
          verify(observer, times(1)).onComplete();
      }
  
      @Test
      public void takeLast1() {
          Observable<String> w = Observable.just("one", "two", "three");
          Observable<String> take = w.takeLast(2);
  
          Observer<String> observer = TestHelper.mockObserver();
          InOrder inOrder = inOrder(observer);
          take.subscribe(observer);
          inOrder.verify(observer, times(1)).onNext("two");
          inOrder.verify(observer, times(1)).onNext("three");
          verify(observer, never()).onNext("one");
          verify(observer, never()).onError(any(Throwable.class));
          verify(observer, times(1)).onComplete();
      }
  
      @Test
      public void takeLast2() {
          Observable<String> w = Observable.just("one");
          Observable<String> take = w.takeLast(10);
  
          Observer<String> observer = TestHelper.mockObserver();
          take.subscribe(observer);
          verify(observer, times(1)).onNext("one");
          verify(observer, never()).onError(any(Throwable.class));
          verify(observer, times(1)).onComplete();
      }
  
      @Test
      public void takeLastWithZeroCount() {
          Observable<String> w = Observable.just("one");
          Observable<String> take = w.takeLast(0);
  
          Observer<String> observer = TestHelper.mockObserver();
          take.subscribe(observer);
          verify(observer, never()).onNext("one");
          verify(observer, never()).onError(any(Throwable.class));
          verify(observer, times(1)).onComplete();
      }
  
      @Test(expected = IllegalArgumentException.class)
      public void takeLastWithNegativeCount() {
          Observable.just("one").takeLast(-1);
      }
  
      @Test
      public void backpressure1() {
          TestObserver<Integer> to = new TestObserver<>();
          Observable.range(1, 100000).takeLast(1)
          .observeOn(Schedulers.newThread())
          .map(newSlowProcessor()).subscribe(to);
          to.awaitDone(5, TimeUnit.SECONDS);
          to.assertNoErrors();
          to.assertValue(100000);
      }
  
      @Test
      public void backpressure2() {
          TestObserver<Integer> to = new TestObserver<>();
          Observable.range(1, 100000).takeLast(Flowable.bufferSize() * 4)
          .observeOn(Schedulers.newThread()).map(newSlowProcessor()).subscribe(to);
          to.awaitDone(5, TimeUnit.SECONDS);
          to.assertNoErrors();
          assertEquals(Flowable.bufferSize() * 4, to.values().size());
      }
  
      private Function<Integer, Integer> newSlowProcessor() {
          return new Function<Integer, Integer>() {
              int c;
  
              @Override
              public Integer apply(Integer i) {
                  if (c++ < 100) {
                      try {
                          Thread.sleep(1);
                      } catch (InterruptedException e) {
                      }
                  }
                  return i;
              }
  
          };
      }
  
      @Test
      public void issue1522() {
          // https://github.com/ReactiveX/RxJava/issues/1522
          assertNull(Observable
                  .empty()
                  .count()
                  .filter(new Predicate<Long>() {
                      @Override
                      public boolean test(Long v) {
                          return false;
                      }
                  })
                  .blockingGet());
      }
  
      @Test
      public void unsubscribeTakesEffectEarlyOnFastPath() {
          final AtomicInteger count = new AtomicInteger();
          Observable.range(0, 100000).takeLast(100000).subscribe(new DefaultObserver<Integer>() {
  
              @Override
              public void onStart() {
              }
  
              @Override
              public void onComplete() {
  
              }
  
              @Override
              public void onError(Throwable e) {
              }
  
              @Override
              public void onNext(Integer integer) {
                  count.incrementAndGet();
                  cancel();
              }
          });
          assertEquals(1, count.get());
      }
  
      @Test
      public void dispose() {
          TestHelper.checkDisposed(Observable.range(1, 10).takeLast(5));
      }
  
      @Test
      public void doubleOnSubscribe() {
          TestHelper.checkDoubleOnSubscribeObservable(new Function<Observable<Object>, ObservableSource<Object>>() {
              @Override
              public ObservableSource<Object> apply(Observable<Object> o) throws Exception {
                  return o.takeLast(5);
              }
          });
      }
  
      @Test
      public void error() {
          Observable.error(new TestException())
          .takeLast(5)
          .test()
          .assertFailure(TestException.class);
      }
  
      @Test
      public void takeLastTake() {
          Observable.range(1, 10)
          .takeLast(5)
          .take(2)
          .test()
          .assertResult(6, 7);
      }
  }
  