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.single;
  
  import static org.junit.Assert.assertEquals;
  
  import org.junit.Test;
  
  import io.reactivex.rxjava3.core.*;
  import io.reactivex.rxjava3.exceptions.TestException;
  import io.reactivex.rxjava3.functions.*;
  import io.reactivex.rxjava3.observers.TestObserver;
  import io.reactivex.rxjava3.subjects.SingleSubject;
  import io.reactivex.rxjava3.testsupport.TestHelper;
  
  public class SingleFlatMapBiSelectorTest extends RxJavaTest {
  
      BiFunction<Integer, Integer, String> stringCombine() {
          return new BiFunction<Integer, Integer, String>() {
              @Override
              public String apply(Integer a, Integer b) throws Exception {
                  return a + ":" + b;
              }
          };
      }
  
      @Test
      public void normal() {
          Single.just(1)
          .flatMap(new Function<Integer, SingleSource<Integer>>() {
              @Override
              public SingleSource<Integer> apply(Integer v) throws Exception {
                  return Single.just(2);
              }
          }, stringCombine())
          .test()
          .assertResult("1:2");
      }
  
      @Test
      public void errorWithJust() {
          final int[] call = { 0 };
  
          Single.<Integer>error(new TestException())
          .flatMap(new Function<Integer, SingleSource<Integer>>() {
              @Override
              public SingleSource<Integer> apply(Integer v) throws Exception {
                  call[0]++;
                  return Single.just(1);
              }
          }, stringCombine())
          .test()
          .assertFailure(TestException.class);
  
          assertEquals(0, call[0]);
      }
  
      @Test
      public void justWithError() {
          final int[] call = { 0 };
  
          Single.just(1)
          .flatMap(new Function<Integer, SingleSource<Integer>>() {
              @Override
              public SingleSource<Integer> apply(Integer v) throws Exception {
                  call[0]++;
                  return Single.<Integer>error(new TestException());
              }
          }, stringCombine())
          .test()
          .assertFailure(TestException.class);
  
          assertEquals(1, call[0]);
      }
  
      @Test
      public void dispose() {
          TestHelper.checkDisposed(SingleSubject.create()
                  .flatMap(new Function<Object, SingleSource<Integer>>() {
              @Override
              public SingleSource<Integer> apply(Object v) throws Exception {
                  return Single.just(1);
              }
          }, new BiFunction<Object, Integer, Object>() {
              @Override
              public Object apply(Object a, Integer b) throws Exception {
                  return b;
              }
          }));
      }
  
      @Test
      public void doubleOnSubscribe() {
          TestHelper.checkDoubleOnSubscribeSingle(new Function<Single<Object>, SingleSource<Object>>() {
              @Override
              public SingleSource<Object> apply(Single<Object> v) throws Exception {
                  return v.flatMap(new Function<Object, SingleSource<Integer>>() {
                      @Override
                      public SingleSource<Integer> apply(Object v) throws Exception {
                          return Single.just(1);
                      }
                  }, new BiFunction<Object, Integer, Object>() {
                      @Override
                      public Object apply(Object a, Integer b) throws Exception {
                          return b;
                      }
                  });
              }
          });
      }
  
      @Test
      public void mapperThrows() {
          Single.just(1)
          .flatMap(new Function<Integer, SingleSource<Integer>>() {
              @Override
              public SingleSource<Integer> apply(Integer v) throws Exception {
                  throw new TestException();
              }
          }, stringCombine())
          .test()
          .assertFailure(TestException.class);
      }
  
      @Test
      public void mapperReturnsNull() {
          Single.just(1)
          .flatMap(new Function<Integer, SingleSource<Integer>>() {
              @Override
              public SingleSource<Integer> apply(Integer v) throws Exception {
                  return null;
              }
          }, stringCombine())
          .test()
          .assertFailure(NullPointerException.class);
      }
  
      @Test
      public void resultSelectorThrows() {
          Single.just(1)
          .flatMap(new Function<Integer, SingleSource<Integer>>() {
              @Override
              public SingleSource<Integer> apply(Integer v) throws Exception {
                  return Single.just(2);
              }
          }, new BiFunction<Integer, Integer, Object>() {
              @Override
              public Object apply(Integer a, Integer b) throws Exception {
                  throw new TestException();
              }
          })
          .test()
          .assertFailure(TestException.class);
      }
  
      @Test
      public void resultSelectorReturnsNull() {
          Single.just(1)
          .flatMap(new Function<Integer, SingleSource<Integer>>() {
              @Override
              public SingleSource<Integer> apply(Integer v) throws Exception {
                  return Single.just(2);
              }
          }, new BiFunction<Integer, Integer, Object>() {
              @Override
              public Object apply(Integer a, Integer b) throws Exception {
                  return null;
              }
          })
          .test()
          .assertFailure(NullPointerException.class);
      }
  
      @Test
      public void mapperCancels() {
          final TestObserver<Integer> to = new TestObserver<>();
  
          Single.just(1)
          .flatMap(new Function<Integer, SingleSource<Integer>>() {
              @Override
              public SingleSource<Integer> apply(Integer v) throws Exception {
                  to.dispose();
                  return Single.just(2);
              }
          }, new BiFunction<Integer, Integer, Integer>() {
              @Override
              public Integer apply(Integer a, Integer b) throws Exception {
                  throw new IllegalStateException();
              }
          })
          .subscribeWith(to)
          .assertEmpty();
      }
  }
  