ObservableTests.java

/**
 * Copyright 2014 Netflix, Inc.
 * 
 * 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 rx;

import static org.junit.Assert.*;
import static org.mockito.Matchers.*;
import static org.mockito.Mockito.*;

import java.lang.Thread.UncaughtExceptionHandler;
import java.util.*;
import java.util.concurrent.*;
import java.util.concurrent.atomic.*;

import org.junit.*;
import org.mockito.*;

import rx.Observable.*;
import rx.exceptions.OnErrorNotImplementedException;
import rx.functions.*;
import rx.observables.ConnectableObservable;
import rx.observers.TestSubscriber;
import rx.schedulers.*;
import rx.subjects.*;
import rx.subscriptions.BooleanSubscription;

public class ObservableTests {

    @Mock
    Observer<Integer> w;

    private static final Func1<Integer, Boolean> IS_EVEN = new Func1<Integer, Boolean>() {
        @Override
        public Boolean call(Integer value) {
            return value % 2 == 0;
        }
    };

    @Before
    public void before() {
        MockitoAnnotations.initMocks(this);
    }

    @Test
    public void fromArray() {
        String[] items = new String[] { "one", "two", "three" };
        assertEquals(new Integer(3), Observable.from(items).count().toBlocking().single());
        assertEquals("two", Observable.from(items).skip(1).take(1).toBlocking().single());
        assertEquals("three", Observable.from(items).takeLast(1).toBlocking().single());
    }

    @Test
    public void fromIterable() {
        ArrayList<String> items = new ArrayList<String>();
        items.add("one");
        items.add("two");
        items.add("three");

        assertEquals(new Integer(3), Observable.from(items).count().toBlocking().single());
        assertEquals("two", Observable.from(items).skip(1).take(1).toBlocking().single());
        assertEquals("three", Observable.from(items).takeLast(1).toBlocking().single());
    }

    @Test
    public void fromArityArgs3() {
        Observable<String> items = Observable.just("one", "two", "three");

        assertEquals(new Integer(3), items.count().toBlocking().single());
        assertEquals("two", items.skip(1).take(1).toBlocking().single());
        assertEquals("three", items.takeLast(1).toBlocking().single());
    }

    @Test
    public void fromArityArgs1() {
        Observable<String> items = Observable.just("one");

        assertEquals(new Integer(1), items.count().toBlocking().single());
        assertEquals("one", items.takeLast(1).toBlocking().single());
    }

    @Test
    public void testCreate() {

        Observable<String> observable = Observable.create(new OnSubscribe<String>() {

            @Override
            public void call(Subscriber<? super String> Observer) {
                Observer.onNext("one");
                Observer.onNext("two");
                Observer.onNext("three");
                Observer.onCompleted();
            }

        });

        @SuppressWarnings("unchecked")
        Observer<String> observer = mock(Observer.class);
        observable.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)).onCompleted();
    }

    @Test
    public void testCountAFewItems() {
        Observable<String> observable = Observable.just("a", "b", "c", "d");
        observable.count().subscribe(w);
        // we should be called only once
        verify(w, times(1)).onNext(anyInt());
        verify(w).onNext(4);
        verify(w, never()).onError(any(Throwable.class));
        verify(w, times(1)).onCompleted();
    }

    @Test
    public void testCountZeroItems() {
        Observable<String> observable = Observable.empty();
        observable.count().subscribe(w);
        // we should be called only once
        verify(w, times(1)).onNext(anyInt());
        verify(w).onNext(0);
        verify(w, never()).onError(any(Throwable.class));
        verify(w, times(1)).onCompleted();
    }

    @Test
    public void testCountError() {
        Observable<String> o = Observable.create(new OnSubscribe<String>() {
            @Override
            public void call(Subscriber<? super String> obsv) {
                obsv.onError(new RuntimeException());
            }
        });
        o.count().subscribe(w);
        verify(w, never()).onNext(anyInt());
        verify(w, never()).onCompleted();
        verify(w, times(1)).onError(any(RuntimeException.class));
    }

    public void testTakeFirstWithPredicateOfSome() {
        Observable<Integer> observable = Observable.just(1, 3, 5, 4, 6, 3);
        observable.takeFirst(IS_EVEN).subscribe(w);
        verify(w, times(1)).onNext(anyInt());
        verify(w).onNext(4);
        verify(w, times(1)).onCompleted();
        verify(w, never()).onError(any(Throwable.class));
    }

    @Test
    public void testTakeFirstWithPredicateOfNoneMatchingThePredicate() {
        Observable<Integer> observable = Observable.just(1, 3, 5, 7, 9, 7, 5, 3, 1);
        observable.takeFirst(IS_EVEN).subscribe(w);
        verify(w, never()).onNext(anyInt());
        verify(w, times(1)).onCompleted();
        verify(w, never()).onError(any(Throwable.class));
    }

    @Test
    public void testTakeFirstOfSome() {
        Observable<Integer> observable = Observable.just(1, 2, 3);
        observable.take(1).subscribe(w);
        verify(w, times(1)).onNext(anyInt());
        verify(w).onNext(1);
        verify(w, times(1)).onCompleted();
        verify(w, never()).onError(any(Throwable.class));
    }

    @Test
    public void testTakeFirstOfNone() {
        Observable<Integer> observable = Observable.empty();
        observable.take(1).subscribe(w);
        verify(w, never()).onNext(anyInt());
        verify(w, times(1)).onCompleted();
        verify(w, never()).onError(any(Throwable.class));
    }

    @Test
    public void testFirstOfNone() {
        Observable<Integer> observable = Observable.empty();
        observable.first().subscribe(w);
        verify(w, never()).onNext(anyInt());
        verify(w, never()).onCompleted();
        verify(w, times(1)).onError(isA(NoSuchElementException.class));
    }

    @Test
    public void testFirstWithPredicateOfNoneMatchingThePredicate() {
        Observable<Integer> observable = Observable.just(1, 3, 5, 7, 9, 7, 5, 3, 1);
        observable.first(IS_EVEN).subscribe(w);
        verify(w, never()).onNext(anyInt());
        verify(w, never()).onCompleted();
        verify(w, times(1)).onError(isA(NoSuchElementException.class));
    }

    @Test
    public void testReduce() {
        Observable<Integer> observable = Observable.just(1, 2, 3, 4);
        observable.reduce(new Func2<Integer, Integer, Integer>() {

            @Override
            public Integer call(Integer t1, Integer t2) {
                return t1 + t2;
            }

        }).subscribe(w);
        // we should be called only once
        verify(w, times(1)).onNext(anyInt());
        verify(w).onNext(10);
    }

    /**
     * A reduce should fail with an NoSuchElementException if done on an empty Observable.
     */
    @Test(expected = NoSuchElementException.class)
    public void testReduceWithEmptyObservable() {
        Observable<Integer> observable = Observable.range(1, 0);
        observable.reduce(new Func2<Integer, Integer, Integer>() {

            @Override
            public Integer call(Integer t1, Integer t2) {
                return t1 + t2;
            }

        }).toBlocking().forEach(new Action1<Integer>() {

            @Override
            public void call(Integer t1) {
                // do nothing ... we expect an exception instead
            }
        });

        fail("Expected an exception to be thrown");
    }

    /**
     * A reduce on an empty Observable and a seed should just pass the seed through.
     * 
     * This is confirmed at https://github.com/ReactiveX/RxJava/issues/423#issuecomment-27642456
     */
    @Test
    public void testReduceWithEmptyObservableAndSeed() {
        Observable<Integer> observable = Observable.range(1, 0);
        int value = observable.reduce(1, new Func2<Integer, Integer, Integer>() {

            @Override
            public Integer call(Integer t1, Integer t2) {
                return t1 + t2;
            }

        }).toBlocking().last();

        assertEquals(1, value);
    }

    @Test
    public void testReduceWithInitialValue() {
        Observable<Integer> observable = Observable.just(1, 2, 3, 4);
        observable.reduce(50, new Func2<Integer, Integer, Integer>() {

            @Override
            public Integer call(Integer t1, Integer t2) {
                return t1 + t2;
            }

        }).subscribe(w);
        // we should be called only once
        verify(w, times(1)).onNext(anyInt());
        verify(w).onNext(60);
    }

    @Test
    public void testOnSubscribeFails() {
        @SuppressWarnings("unchecked")
        Observer<String> observer = mock(Observer.class);
        final RuntimeException re = new RuntimeException("bad impl");
        Observable<String> o = Observable.create(new OnSubscribe<String>() {

            @Override
            public void call(Subscriber<? super String> t1) {
                throw re;
            }

        });
        o.subscribe(observer);
        verify(observer, times(0)).onNext(anyString());
        verify(observer, times(0)).onCompleted();
        verify(observer, times(1)).onError(re);
    }

    @Test
    public void testMaterializeDematerializeChaining() {
        Observable<Integer> obs = Observable.just(1);
        Observable<Integer> chained = obs.materialize().dematerialize();

        @SuppressWarnings("unchecked")
        Observer<Integer> observer = mock(Observer.class);
        chained.subscribe(observer);

        verify(observer, times(1)).onNext(1);
        verify(observer, times(1)).onCompleted();
        verify(observer, times(0)).onError(any(Throwable.class));
    }

    /**
     * The error from the user provided Observer is not handled by the subscribe method try/catch.
     * 
     * It is handled by the AtomicObserver that wraps the provided Observer.
     * 
     * Result: Passes (if AtomicObserver functionality exists)
     */
    @Test
    public void testCustomObservableWithErrorInObserverAsynchronous() throws InterruptedException {
        final CountDownLatch latch = new CountDownLatch(1);
        final AtomicInteger count = new AtomicInteger();
        final AtomicReference<Throwable> error = new AtomicReference<Throwable>();
        Observable.create(new OnSubscribe<String>() {

            @Override
            public void call(final Subscriber<? super String> observer) {
                final BooleanSubscription s = new BooleanSubscription();
                new Thread(new Runnable() {

                    @Override
                    public void run() {
                        try {
                            if (!s.isUnsubscribed()) {
                                observer.onNext("1");
                                observer.onNext("2");
                                observer.onNext("three");
                                observer.onNext("4");
                                observer.onCompleted();
                            }
                        } finally {
                            latch.countDown();
                        }
                    }
                }).start();
            }
        }).subscribe(new Subscriber<String>() {
            @Override
            public void onCompleted() {
                System.out.println("completed");
            }

            @Override
            public void onError(Throwable e) {
                error.set(e);
                System.out.println("error");
                e.printStackTrace();
            }

            @Override
            public void onNext(String v) {
                int num = Integer.parseInt(v);
                System.out.println(num);
                // doSomething(num);
                count.incrementAndGet();
            }

        });

        // wait for async sequence to complete
        latch.await();

        assertEquals(2, count.get());
        assertNotNull(error.get());
        if (!(error.get() instanceof NumberFormatException)) {
            fail("It should be a NumberFormatException");
        }
    }

    /**
     * The error from the user provided Observer is handled by the subscribe try/catch because this is synchronous
     * 
     * Result: Passes
     */
    @Test
    public void testCustomObservableWithErrorInObserverSynchronous() {
        final AtomicInteger count = new AtomicInteger();
        final AtomicReference<Throwable> error = new AtomicReference<Throwable>();
        Observable.create(new OnSubscribe<String>() {

            @Override
            public void call(Subscriber<? super String> observer) {
                observer.onNext("1");
                observer.onNext("2");
                observer.onNext("three");
                observer.onNext("4");
                observer.onCompleted();
            }
        }).subscribe(new Subscriber<String>() {

            @Override
            public void onCompleted() {
                System.out.println("completed");
            }

            @Override
            public void onError(Throwable e) {
                error.set(e);
                System.out.println("error");
                e.printStackTrace();
            }

            @Override
            public void onNext(String v) {
                int num = Integer.parseInt(v);
                System.out.println(num);
                // doSomething(num);
                count.incrementAndGet();
            }

        });
        assertEquals(2, count.get());
        assertNotNull(error.get());
        if (!(error.get() instanceof NumberFormatException)) {
            fail("It should be a NumberFormatException");
        }
    }

    /**
     * The error from the user provided Observable is handled by the subscribe try/catch because this is synchronous
     * 
     * 
     * Result: Passes
     */
    @Test
    public void testCustomObservableWithErrorInObservableSynchronous() {
        final AtomicInteger count = new AtomicInteger();
        final AtomicReference<Throwable> error = new AtomicReference<Throwable>();
        Observable.create(new OnSubscribe<String>() {

            @Override
            public void call(Subscriber<? super String> observer) {
                observer.onNext("1");
                observer.onNext("2");
                throw new NumberFormatException();
            }
        }).subscribe(new Subscriber<String>() {

            @Override
            public void onCompleted() {
                System.out.println("completed");
            }

            @Override
            public void onError(Throwable e) {
                error.set(e);
                System.out.println("error");
                e.printStackTrace();
            }

            @Override
            public void onNext(String v) {
                System.out.println(v);
                count.incrementAndGet();
            }

        });
        assertEquals(2, count.get());
        assertNotNull(error.get());
        if (!(error.get() instanceof NumberFormatException)) {
            fail("It should be a NumberFormatException");
        }
    }

    @Test
    public void testPublishLast() throws InterruptedException {
        final AtomicInteger count = new AtomicInteger();
        ConnectableObservable<String> connectable = Observable.create(new OnSubscribe<String>() {
            @Override
            public void call(final Subscriber<? super String> observer) {
                count.incrementAndGet();
                new Thread(new Runnable() {
                    @Override
                    public void run() {
                        observer.onNext("first");
                        observer.onNext("last");
                        observer.onCompleted();
                    }
                }).start();
            }
        }).takeLast(1).publish();

        // subscribe once
        final CountDownLatch latch = new CountDownLatch(1);
        connectable.subscribe(new Action1<String>() {
            @Override
            public void call(String value) {
                assertEquals("last", value);
                latch.countDown();
            }
        });

        // subscribe twice
        connectable.subscribe(new Action1<String>() {
            @Override
            public void call(String ignored) {
            }
        });

        Subscription subscription = connectable.connect();
        assertTrue(latch.await(1000, TimeUnit.MILLISECONDS));
        assertEquals(1, count.get());
        subscription.unsubscribe();
    }

    @Test
    public void testReplay() throws InterruptedException {
        final AtomicInteger counter = new AtomicInteger();
        ConnectableObservable<String> o = Observable.create(new OnSubscribe<String>() {

            @Override
            public void call(final Subscriber<? super String> observer) {
                new Thread(new Runnable() {

                    @Override
                    public void run() {
                        counter.incrementAndGet();
                        observer.onNext("one");
                        observer.onCompleted();
                    }
                }).start();
            }
        }).replay();

        // we connect immediately and it will emit the value
        Subscription s = o.connect();
        try {

            // we then expect the following 2 subscriptions to get that same value
            final CountDownLatch latch = new CountDownLatch(2);

            // subscribe once
            o.subscribe(new Action1<String>() {

                @Override
                public void call(String v) {
                    assertEquals("one", v);
                    latch.countDown();
                }
            });

            // subscribe again
            o.subscribe(new Action1<String>() {

                @Override
                public void call(String v) {
                    assertEquals("one", v);
                    latch.countDown();
                }
            });

            if (!latch.await(1000, TimeUnit.MILLISECONDS)) {
                fail("subscriptions did not receive values");
            }
            assertEquals(1, counter.get());
        } finally {
            s.unsubscribe();
        }
    }

    @Test
    public void testCache() throws InterruptedException {
        final AtomicInteger counter = new AtomicInteger();
        Observable<String> o = Observable.create(new OnSubscribe<String>() {

            @Override
            public void call(final Subscriber<? super String> observer) {
                new Thread(new Runnable() {

                    @Override
                    public void run() {
                        counter.incrementAndGet();
                        observer.onNext("one");
                        observer.onCompleted();
                    }
                }).start();
            }
        }).cache();

        // we then expect the following 2 subscriptions to get that same value
        final CountDownLatch latch = new CountDownLatch(2);

        // subscribe once
        o.subscribe(new Action1<String>() {

            @Override
            public void call(String v) {
                assertEquals("one", v);
                latch.countDown();
            }
        });

        // subscribe again
        o.subscribe(new Action1<String>() {

            @Override
            public void call(String v) {
                assertEquals("one", v);
                latch.countDown();
            }
        });

        if (!latch.await(1000, TimeUnit.MILLISECONDS)) {
            fail("subscriptions did not receive values");
        }
        assertEquals(1, counter.get());
    }

    @Test
    public void testCacheWithCapacity() throws InterruptedException {
        final AtomicInteger counter = new AtomicInteger();
        Observable<String> o = Observable.create(new OnSubscribe<String>() {

            @Override
            public void call(final Subscriber<? super String> observer) {
                new Thread(new Runnable() {

                    @Override
                    public void run() {
                        counter.incrementAndGet();
                        observer.onNext("one");
                        observer.onCompleted();
                    }
                }).start();
            }
        }).cacheWithInitialCapacity(1);

        // we then expect the following 2 subscriptions to get that same value
        final CountDownLatch latch = new CountDownLatch(2);

        // subscribe once
        o.subscribe(new Action1<String>() {

            @Override
            public void call(String v) {
                assertEquals("one", v);
                latch.countDown();
            }
        });

        // subscribe again
        o.subscribe(new Action1<String>() {

            @Override
            public void call(String v) {
                assertEquals("one", v);
                latch.countDown();
            }
        });

        if (!latch.await(1000, TimeUnit.MILLISECONDS)) {
            fail("subscriptions did not receive values");
        }
        assertEquals(1, counter.get());
    }

    /**
     * https://github.com/ReactiveX/RxJava/issues/198
     * 
     * Rx Design Guidelines 5.2
     * 
     * "when calling the Subscribe method that only has an onNext argument, the OnError behavior will be
     * to rethrow the exception on the thread that the message comes out from the Observable.
     * The OnCompleted behavior in this case is to do nothing."
     */
    @Test
    public void testErrorThrownWithoutErrorHandlerSynchronous() {
        try {
            Observable.error(new RuntimeException("failure")).subscribe(new Action1<Object>() {

                @Override
                public void call(Object t1) {
                    // won't get anything
                }

            });
            fail("expected exception");
        } catch (Throwable e) {
            assertEquals("failure", e.getMessage());
        }
    }

    /**
     * https://github.com/ReactiveX/RxJava/issues/198
     * 
     * Rx Design Guidelines 5.2
     * 
     * "when calling the Subscribe method that only has an onNext argument, the OnError behavior will be
     * to rethrow the exception on the thread that the message comes out from the Observable.
     * The OnCompleted behavior in this case is to do nothing."
     * 
     * @throws InterruptedException
     */
    @Test
    public void testErrorThrownWithoutErrorHandlerAsynchronous() throws InterruptedException {
        final CountDownLatch latch = new CountDownLatch(1);
        final AtomicReference<Throwable> exception = new AtomicReference<Throwable>();
        Observable.create(new OnSubscribe<String>() {

            @Override
            public void call(final Subscriber<? super String> observer) {
                new Thread(new Runnable() {

                    @Override
                    public void run() {
                        try {
                            observer.onError(new Error("failure"));
                        } catch (Throwable e) {
                            // without an onError handler it has to just throw on whatever thread invokes it
                            exception.set(e);
                        }
                        latch.countDown();
                    }
                }).start();
            }
        }).subscribe(new Action1<String>() {

            @Override
            public void call(String t1) {

            }

        });
        // wait for exception
        latch.await(3000, TimeUnit.MILLISECONDS);
        assertNotNull(exception.get());
        assertEquals("failure", exception.get().getMessage());
    }

    @Test
    public void testTakeWithErrorInObserver() {
        final AtomicInteger count = new AtomicInteger();
        final AtomicReference<Throwable> error = new AtomicReference<Throwable>();
        Observable.just("1", "2", "three", "4").take(3).subscribe(new Subscriber<String>() {

            @Override
            public void onCompleted() {
                System.out.println("completed");
            }

            @Override
            public void onError(Throwable e) {
                error.set(e);
                System.out.println("error");
                e.printStackTrace();
            }

            @Override
            public void onNext(String v) {
                int num = Integer.parseInt(v);
                System.out.println(num);
                // doSomething(num);
                count.incrementAndGet();
            }

        });
        assertEquals(2, count.get());
        assertNotNull(error.get());
        if (!(error.get() instanceof NumberFormatException)) {
            fail("It should be a NumberFormatException");
        }
    }

    @Test
    public void testOfType() {
        Observable<String> observable = Observable.just(1, "abc", false, 2L).ofType(String.class);

        @SuppressWarnings("unchecked")
        Observer<Object> observer = mock(Observer.class);
        observable.subscribe(observer);
        verify(observer, never()).onNext(1);
        verify(observer, times(1)).onNext("abc");
        verify(observer, never()).onNext(false);
        verify(observer, never()).onNext(2L);
        verify(observer, never()).onError(
                org.mockito.Matchers.any(Throwable.class));
        verify(observer, times(1)).onCompleted();
    }

    @Test
    public void testOfTypeWithPolymorphism() {
        ArrayList<Integer> l1 = new ArrayList<Integer>();
        l1.add(1);
        LinkedList<Integer> l2 = new LinkedList<Integer>();
        l2.add(2);

        @SuppressWarnings("rawtypes")
        Observable<List> observable = Observable.<Object> just(l1, l2, "123").ofType(List.class);

        @SuppressWarnings("unchecked")
        Observer<Object> observer = mock(Observer.class);
        observable.subscribe(observer);
        verify(observer, times(1)).onNext(l1);
        verify(observer, times(1)).onNext(l2);
        verify(observer, never()).onNext("123");
        verify(observer, never()).onError(
                org.mockito.Matchers.any(Throwable.class));
        verify(observer, times(1)).onCompleted();
    }

    @Test
    public void testContains() {
        Observable<Boolean> observable = Observable.just("a", "b", null).contains("b");

        @SuppressWarnings("unchecked")
        Observer<Object> observer = mock(Observer.class);
        observable.subscribe(observer);
        verify(observer, times(1)).onNext(true);
        verify(observer, never()).onNext(false);
        verify(observer, never()).onError(
                org.mockito.Matchers.any(Throwable.class));
        verify(observer, times(1)).onCompleted();
    }

    @Test
    public void testContainsWithInexistence() {
        Observable<Boolean> observable = Observable.just("a", "b", null).contains("c");

        @SuppressWarnings("unchecked")
        Observer<Object> observer = mock(Observer.class);
        observable.subscribe(observer);
        verify(observer, times(1)).onNext(false);
        verify(observer, never()).onNext(true);
        verify(observer, never()).onError(
                org.mockito.Matchers.any(Throwable.class));
        verify(observer, times(1)).onCompleted();
    }

    @Test
    public void testContainsWithNull() {
        Observable<Boolean> observable = Observable.just("a", "b", null).contains(null);

        @SuppressWarnings("unchecked")
        Observer<Object> observer = mock(Observer.class);
        observable.subscribe(observer);
        verify(observer, times(1)).onNext(true);
        verify(observer, never()).onNext(false);
        verify(observer, never()).onError(
                org.mockito.Matchers.any(Throwable.class));
        verify(observer, times(1)).onCompleted();
    }

    @Test
    public void testContainsWithEmptyObservable() {
        Observable<Boolean> observable = Observable.<String> empty().contains("a");

        @SuppressWarnings("unchecked")
        Observer<Object> observer = mock(Observer.class);
        observable.subscribe(observer);
        verify(observer, times(1)).onNext(false);
        verify(observer, never()).onNext(true);
        verify(observer, never()).onError(
                org.mockito.Matchers.any(Throwable.class));
        verify(observer, times(1)).onCompleted();
    }

    @Test
    public void testIgnoreElements() {
        Observable<Integer> observable = Observable.just(1, 2, 3).ignoreElements();

        @SuppressWarnings("unchecked")
        Observer<Integer> observer = mock(Observer.class);
        observable.subscribe(observer);
        verify(observer, never()).onNext(any(Integer.class));
        verify(observer, never()).onError(any(Throwable.class));
        verify(observer, times(1)).onCompleted();
    }

    @Test
            public void testJustWithScheduler() {
                TestScheduler scheduler = new TestScheduler();
                Observable<Integer> observable = Observable.from(Arrays.asList(1, 2)).subscribeOn(scheduler);
        
                @SuppressWarnings("unchecked")
                Observer<Integer> observer = mock(Observer.class);
                observable.subscribe(observer);
        
                scheduler.advanceTimeBy(1, TimeUnit.MILLISECONDS);
        
                InOrder inOrder = inOrder(observer);
                inOrder.verify(observer, times(1)).onNext(1);
                inOrder.verify(observer, times(1)).onNext(2);
                inOrder.verify(observer, times(1)).onCompleted();
                inOrder.verifyNoMoreInteractions();
            }

    @Test
    public void testStartWithWithScheduler() {
        TestScheduler scheduler = new TestScheduler();
        Observable<Integer> observable = Observable.just(3, 4).startWith(Arrays.asList(1, 2)).subscribeOn(scheduler);

        @SuppressWarnings("unchecked")
        Observer<Integer> observer = mock(Observer.class);
        observable.subscribe(observer);

        scheduler.advanceTimeBy(1, TimeUnit.MILLISECONDS);

        InOrder inOrder = inOrder(observer);
        inOrder.verify(observer, times(1)).onNext(1);
        inOrder.verify(observer, times(1)).onNext(2);
        inOrder.verify(observer, times(1)).onNext(3);
        inOrder.verify(observer, times(1)).onNext(4);
        inOrder.verify(observer, times(1)).onCompleted();
        inOrder.verifyNoMoreInteractions();
    }

    @Test
    public void testRangeWithScheduler() {
        TestScheduler scheduler = new TestScheduler();
        Observable<Integer> observable = Observable.range(3, 4, scheduler);

        @SuppressWarnings("unchecked")
        Observer<Integer> observer = mock(Observer.class);
        observable.subscribe(observer);

        scheduler.advanceTimeBy(1, TimeUnit.MILLISECONDS);

        InOrder inOrder = inOrder(observer);
        inOrder.verify(observer, times(1)).onNext(3);
        inOrder.verify(observer, times(1)).onNext(4);
        inOrder.verify(observer, times(1)).onNext(5);
        inOrder.verify(observer, times(1)).onNext(6);
        inOrder.verify(observer, times(1)).onCompleted();
        inOrder.verifyNoMoreInteractions();
    }

    @Test
    public void testCollectToList() {
        Observable<List<Integer>> o = Observable.just(1, 2, 3).collect(new Func0<List<Integer>>() {

            @Override
            public List<Integer> call() {
                return new ArrayList<Integer>();
            }
            
        }, new Action2<List<Integer>, Integer>() {

            @Override
            public void call(List<Integer> list, Integer v) {
                list.add(v);
            }
        });
        
        List<Integer> list =  o.toBlocking().last();

        assertEquals(3, list.size());
        assertEquals(1, list.get(0).intValue());
        assertEquals(2, list.get(1).intValue());
        assertEquals(3, list.get(2).intValue());
        
        // test multiple subscribe
        List<Integer> list2 =  o.toBlocking().last();

        assertEquals(3, list2.size());
        assertEquals(1, list2.get(0).intValue());
        assertEquals(2, list2.get(1).intValue());
        assertEquals(3, list2.get(2).intValue());
    }

    @Test
    public void testCollectToString() {
        String value = Observable.just(1, 2, 3).collect(new Func0<StringBuilder>() {

            @Override
            public StringBuilder call() {
                return new StringBuilder();
            }
            
        }, new Action2<StringBuilder, Integer>() {

            @Override
            public void call(StringBuilder sb, Integer v) {
                if (sb.length() > 0) {
                    sb.append("-");
                }
                sb.append(v);
            }
        }).toBlocking().last().toString();

        assertEquals("1-2-3", value);
    }
    
    @Test
    public void testMergeWith() {
        TestSubscriber<Integer> ts = new TestSubscriber<Integer>();
        Observable.just(1).mergeWith(Observable.just(2)).subscribe(ts);
        ts.assertReceivedOnNext(Arrays.asList(1, 2));
    }
    
    @Test
    public void testConcatWith() {
        TestSubscriber<Integer> ts = new TestSubscriber<Integer>();
        Observable.just(1).concatWith(Observable.just(2)).subscribe(ts);
        ts.assertReceivedOnNext(Arrays.asList(1, 2));
    }
    
    @Test
    public void testAmbWith() {
        TestSubscriber<Integer> ts = new TestSubscriber<Integer>();
        Observable.just(1).ambWith(Observable.just(2)).subscribe(ts);
        ts.assertReceivedOnNext(Arrays.asList(1));
    }

    @Test(expected = OnErrorNotImplementedException.class)
    public void testSubscribeWithoutOnError() {
        Observable<String> o = Observable.just("a", "b").flatMap(new Func1<String, Observable<String>>() {
            @Override
            public Observable<String> call(String s) {
                return Observable.error(new Exception("test"));
            }
        });
        o.subscribe();
    }

    @Test
    public void testTakeWhileToList() {
        final int expectedCount = 3;
        final AtomicInteger count = new AtomicInteger();
        for (int i = 0;i < expectedCount; i++) {
            Observable
                    .just(Boolean.TRUE, Boolean.FALSE)
                    .takeWhile(new Func1<Boolean, Boolean>() {
                        @Override
                        public Boolean call(Boolean value) {
                            return value;
                        }
                    })
                    .toList()
                    .doOnNext(new Action1<List<Boolean>>() {
                        @Override
                        public void call(List<Boolean> booleans) {
                            count.incrementAndGet();
                        }
                    })
                    .subscribe();
        }
        assertEquals(expectedCount, count.get());
    }
    
    @Test
    public void testCompose() {
        TestSubscriber<String> ts = new TestSubscriber<String>();
        Observable.just(1, 2, 3).compose(new Transformer<Integer, String>() {

            @Override
            public Observable<String> call(Observable<Integer> t1) {
                return t1.map(new Func1<Integer, String>() {
                    
                    @Override
                    public String call(Integer t1) {
                        return String.valueOf(t1);
                    }
                    
                });
            }
            
        }).subscribe(ts);
        ts.assertTerminalEvent();
        ts.assertNoErrors();
        ts.assertReceivedOnNext(Arrays.asList("1", "2", "3"));
    }
    
    @Test
    public void testErrorThrownIssue1685() throws Exception {
        Subject<Object, Object> subject = ReplaySubject.create();

        ExecutorService exec = Executors.newSingleThreadExecutor();
        
        try {
            
            final AtomicReference<Throwable> err = new AtomicReference<Throwable>();
            
            Scheduler s = Schedulers.from(exec);
            exec.submit(new Runnable() {
                @Override
                public void run() {
                    Thread.currentThread().setUncaughtExceptionHandler(new UncaughtExceptionHandler() {
                        @Override
                        public void uncaughtException(Thread t, Throwable e) {
                            err.set(e);
                        }
                    });
                }
            }).get();
            
            subject.subscribe();

            Observable.error(new RuntimeException("oops"))
                .materialize()
                .delay(1, TimeUnit.SECONDS, s)
                .dematerialize()
                .subscribe(subject);
    
            subject.materialize().toBlocking().first();

            for (int i = 0; i < 50 && err.get() == null; i++) {
                Thread.sleep(100); // the uncaught exception comes after the terminal event reaches toBlocking
            }
            
            assertNotNull("UncaughtExceptionHandler didn't get anything.", err.get());
            
            System.out.println("Done");
        } finally {
            exec.shutdownNow();
        }
    }

    @Test
    public void testEmptyIdentity() {
        assertEquals(Observable.empty(), Observable.empty());
    }
    
    @Test
    public void testEmptyIsEmpty() {
        Observable.<Integer>empty().subscribe(w);
        
        verify(w).onCompleted();
        verify(w, never()).onNext(any(Integer.class));
        verify(w, never()).onError(any(Throwable.class));
    }
    
    @Test // cf. https://github.com/ReactiveX/RxJava/issues/2599
    public void testSubscribingSubscriberAsObserverMaintainsSubscriptionChain() {
        TestSubscriber<Object> subscriber = new TestSubscriber<Object>();
        Subscription subscription = Observable.just("event").subscribe((Observer<Object>) subscriber);
        subscription.unsubscribe();

        subscriber.assertUnsubscribed();
    }

    @Test(expected=OnErrorNotImplementedException.class)
    public void testForEachWithError() {
        Observable.error(new Exception("boo"))
        //
        .forEach(new Action1<Object>() {
            @Override
            public void call(Object t) {
                //do nothing
            }});
    }
    
    @Test(expected=IllegalArgumentException.class)
    public void testForEachWithNull() {
        Observable.error(new Exception("boo"))
        //
        .forEach(null);
    }
    
    @Test
    public void testExtend() {
        final TestSubscriber<Object> subscriber = new TestSubscriber<Object>();
        final Object value = new Object();
        Observable.just(value).extend(new Func1<OnSubscribe<Object>,Object>(){
            @Override
            public Object call(OnSubscribe<Object> onSubscribe) {
                onSubscribe.call(subscriber);
                subscriber.assertNoErrors();
                subscriber.assertCompleted();
                subscriber.assertValue(value);
                return subscriber.getOnNextEvents().get(0);
            }});
    }
}