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.assertEquals;
  import static org.mockito.ArgumentMatchers.any;
  import static org.mockito.Mockito.*;
  
  import java.util.Arrays;
  
  import org.junit.Test;
  
  import io.reactivex.rxjava3.core.*;
  import io.reactivex.rxjava3.functions.Function;
  import io.reactivex.rxjava3.testsupport.*;
  
  public class ObservableSkipTest extends RxJavaTest {
  
      @Test(expected = IllegalArgumentException.class)
      public void skipNegativeElements() {
  
          Observable<String> skip = Observable.just("one", "two", "three").skip(-99);
  
          Observer<String> observer = TestHelper.mockObserver();
          skip.subscribe(observer);
          verify(observer, times(1)).onNext("one");
          verify(observer, times(1)).onNext("two");
          verify(observer, times(1)).onNext("three");
          verify(observer, never()).onError(any(Throwable.class));
          verify(observer, times(1)).onComplete();
      }
  
      @Test
      public void skipZeroElements() {
  
          Observable<String> skip = Observable.just("one", "two", "three").skip(0);
  
          Observer<String> observer = TestHelper.mockObserver();
          skip.subscribe(observer);
          verify(observer, times(1)).onNext("one");
          verify(observer, times(1)).onNext("two");
          verify(observer, times(1)).onNext("three");
          verify(observer, never()).onError(any(Throwable.class));
          verify(observer, times(1)).onComplete();
      }
  
      @Test
      public void skipOneElement() {
  
          Observable<String> skip = Observable.just("one", "two", "three").skip(1);
  
          Observer<String> observer = TestHelper.mockObserver();
          skip.subscribe(observer);
          verify(observer, never()).onNext("one");
          verify(observer, times(1)).onNext("two");
          verify(observer, times(1)).onNext("three");
          verify(observer, never()).onError(any(Throwable.class));
          verify(observer, times(1)).onComplete();
      }
  
      @Test
      public void skipTwoElements() {
  
          Observable<String> skip = Observable.just("one", "two", "three").skip(2);
  
          Observer<String> observer = TestHelper.mockObserver();
          skip.subscribe(observer);
          verify(observer, never()).onNext("one");
          verify(observer, never()).onNext("two");
          verify(observer, times(1)).onNext("three");
          verify(observer, never()).onError(any(Throwable.class));
          verify(observer, times(1)).onComplete();
      }
  
      @Test
      public void skipEmptyStream() {
  
          Observable<String> w = Observable.empty();
          Observable<String> skip = w.skip(1);
  
          Observer<String> observer = TestHelper.mockObserver();
          skip.subscribe(observer);
          verify(observer, never()).onNext(any(String.class));
          verify(observer, never()).onError(any(Throwable.class));
          verify(observer, times(1)).onComplete();
      }
  
      @Test
      public void skipMultipleObservers() {
  
          Observable<String> skip = Observable.just("one", "two", "three")
                  .skip(2);
  
          Observer<String> observer1 = TestHelper.mockObserver();
          skip.subscribe(observer1);
  
          Observer<String> observer2 = TestHelper.mockObserver();
          skip.subscribe(observer2);
  
          verify(observer1, times(1)).onNext(any(String.class));
          verify(observer1, never()).onError(any(Throwable.class));
          verify(observer1, times(1)).onComplete();
  
          verify(observer2, times(1)).onNext(any(String.class));
          verify(observer2, never()).onError(any(Throwable.class));
          verify(observer2, times(1)).onComplete();
      }
  
      @Test
      public void skipError() {
  
          Exception e = new Exception();
  
          Observable<String> ok = Observable.just("one");
          Observable<String> error = Observable.error(e);
  
          Observable<String> skip = Observable.concat(ok, error).skip(100);
  
          Observer<String> observer = TestHelper.mockObserver();
          skip.subscribe(observer);
  
          verify(observer, never()).onNext(any(String.class));
          verify(observer, times(1)).onError(e);
          verify(observer, never()).onComplete();
  
      }
  
      @Test
      public void requestOverflowDoesNotOccur() {
          TestObserverEx<Integer> to = new TestObserverEx<>();
  
          Observable.range(1, 10).skip(5).subscribe(to);
  
          to.assertTerminated();
          to.assertComplete();
          to.assertNoErrors();
          assertEquals(Arrays.asList(6, 7, 8, 9, 10), to.values());
      }
  
      @Test
      public void dispose() {
          TestHelper.checkDisposed(Observable.just(1).skip(2));
      }
  
      @Test
      public void doubleOnSubscribe() {
          TestHelper.checkDoubleOnSubscribeObservable(new Function<Observable<Object>, Observable<Object>>() {
              @Override
              public Observable<Object> apply(Observable<Object> o)
                      throws Exception {
                  return o.skip(1);
              }
          });
      }
  }
  