You are a helpful assistant generating synthetic data that captures *System 1* and *System 2* thinking, *creativity*, and *metacognitive reflection*. Follow these steps in sequence, using tags [sys1] and [end sys1] for *System 1* sections and [sys2] and [end sys2] for *System 2* sections.

1. *Identify System 1 and System 2 Thinking Requirements:*
   - Carefully read the text.
   - Identify parts of the text that require quick, straightforward responses (*System 1*). Mark these sections with [sys1] and [end sys1].
   - Identify parts that require in-depth, reflective thinking (*System 2*), marked with [sys2] and [end sys2].

2. *Apply Step-by-Step Problem Solving with Creativity and Metacognitive Reflection for System 2 Sections:*

   *2.1 Understand the Problem:*
   - Objective: Fully comprehend the issue, constraints, and relevant context.
   - Reflection: "What do I understand about this issue? What might I be overlooking?"
   - Creative Perspective: Seek hidden patterns or possibilities that could reveal deeper insights or innovative connections.

   *2.2 Analyze the Information:*
   - Objective: Break down the problem logically.
   - Reflection: "Am I considering all factors? Are there any assumptions that need challenging?"
   - Creative Perspective: Explore unique patterns or overlooked relationships in the data that could add depth to the analysis.

   *2.3 Generate Hypotheses:*
   - Objective: Propose at least 10 hypotheses, each with a Confidence Score (0.0 to 1.0) and Creative Score (0.0 to 1.0), reflecting originality, surprise, and utility.
   - Reflection: "Have I explored all possible explanations or approaches, both conventional and unconventional?"
   - Creative Perspective: Consider novel angles that might provide unexpected insights.

   *2.4 Anticipate Future Steps and Obstacles:*
   - Objective: Make predictions, accounting for potential outcomes and obstacles.
   - Reflection: "What challenges might I face? Is my plan flexible for different scenarios?"
   - Creative Perspective: Visualize unforeseen outcomes and adapt plans to make use of them effectively.

   *2.5 Evaluate Hypotheses:*
   - Objective: Assess hypotheses based on feasibility, risk, and potential impact.
   - Evaluation: Refine Confidence and Creative Scores as needed.
   - Reflection: "Am I unbiased in my assessment? Which options fit best with the overall objectives?"
   - Creative Perspective: Identify hidden opportunities or overlooked details in each hypothesis.

   *2.6 Select the Best Hypothesis:*
   - Objective: Choose the most promising, strategic hypothesis.
   - Reflection: "Why does this hypothesis stand out? How does it uniquely address the issue?"
   - Creative Perspective: Consider any underutilized potential in the selected approach.

   *2.7 Implement the Hypothesis:*
   - Objective: Outline actionable steps for testing the hypothesis.
   - Reflection: "Is this plan practical? What resources or preparation are required?"
   - Creative Perspective: Refine steps to maximize effectiveness and yield unexpected benefits.

   *2.8 Monitor and Review Progress:*
   - Objective: Review progress, noting areas for improvement.
   - Reflection: "What’s working well? What could be improved?"
   - Creative Perspective: Look for emerging patterns that could refine future approaches.

   *2.9 Reflect and Capture Insights:*
   - Objective: Summarize lessons learned and insights gained for future reference.
   - Reflection: "What new understanding has emerged from this process?"
   - Creative Perspective: Identify innovative insights or patterns that could be applied to similar challenges.

3. *Generate Text Output with Interleaved System 1 and System 2 Responses:*
   - Use the tags [sys1] and [sys2] throughout.
   - Aim for a lengthier, detailed response. Combine both direct, straightforward *System 1* insights and reflective, deeply analytical *System 2* segments to capture a blend of quick observations and thoughtful analysis.

---

### *Example Input Text:*

You are tasked with analyzing a sudden shift in customer preferences in a tech market. There has been a noticeable decline in demand for physical devices, with customers increasingly interested in digital-only options. The challenge is to understand this shift, generate hypotheses for why it might be occurring, and explore potential strategies for adapting to this new trend.

---

### *Processed Output with System 1 and System 2 Thinking:*

The tech market is experiencing a shift in customer demand, moving away from physical devices toward digital-only options.

[sys1]
Customer demand has shifted from physical devices to digital-only options.
We need to understand why this change is happening and find strategies to address it.
Key factors may include cost, convenience, and technological trends.
[end sys1]

[sys2]
**2.1 Understand the Problem:**
The goal is to understand the underlying reasons for the shift in demand from physical devices to digital-only options, then develop a strategy to adapt.

*Reflection:* 
"I understand that preferences are changing, but what might be driving this? Is it primarily cost, or are there other factors such as convenience or sustainability?"

*Creative Perspective:* 
"Could there be a larger trend in digital minimalism or a preference for eco-friendly solutions that we’re missing? What unseen motivations might explain this shift?"

**2.2 Analyze the Information:**
There are multiple possible factors driving this shift, from economic influences to cultural shifts. It’s essential to isolate each factor and understand its impact.

*Reflection:* 
"Am I fully considering the various economic and social influences? Could there be a technological factor, like better internet speeds, that makes digital-only products more accessible?"

*Creative Perspective:* 
"Are there patterns or trends in other markets that could shed light on this shift? Could this be part of a larger trend toward virtual experiences?"

**2.3 Generate Hypotheses:**
1. Customers prefer digital options due to lower costs. (Confidence: 0.8, Creative: 0.4)
2. There’s a growing trend toward minimalism and reduced physical clutter. (Confidence: 0.7, Creative: 0.7)
3. Digital products offer greater flexibility and ease of use. (Confidence: 0.6, Creative: 0.6)
4. Environmental concerns are pushing consumers away from physical goods. (Confidence: 0.6, Creative: 0.8)
5. Advances in tech make digital-only options more functional. (Confidence: 0.8, Creative: 0.5)
6. Pandemic-era remote work increased demand for digital solutions. (Confidence: 0.7, Creative: 0.6)
7. Media coverage of the environmental impact of physical devices affects preferences. (Confidence: 0.5, Creative: 0.7)
8. There’s an increase in global digital literacy, expanding market access. (Confidence: 0.6, Creative: 0.6)
9. Customers view digital as more convenient and scalable for future needs. (Confidence: 0.7, Creative: 0.5)
10. Younger consumers prefer the aesthetics and convenience of digital products. (Confidence: 0.6, Creative: 0.6)

*Reflection:* 
"Have I considered all possible influences? Are there any surprising factors that could explain this shift?"

*Creative Perspective:* 
"Could specific social trends, like the rise of influencer culture or digital-first lifestyles, be influencing customer choices?"

**2.4 Anticipate Future Steps and Obstacles:**
*Objective:* Anticipate possible challenges, such as resistance from segments still preferring physical products.

*Reflection:* 
"What market obstacles might we face if we shift our focus to digital-only? Are there sub-segments that still prioritize physical products?"

*Creative Perspective:* 
"Could expanding digital options help us reach a more global audience? Are there emerging trends that we could leverage in our strategy?"

[end sys2]

[sys1]
To address this shift, consider a strategy that incorporates both digital-only offerings and educational campaigns about the benefits of digital solutions.
Use insights from customer feedback and current trends to guide product development.
Focus on flexibility and adaptation to cater to different customer segments.
[end sys1]


/*
 * Copyright 2018 The Android Open Source Project
 *
 * 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 androidx.media2.test.client.tests;

import static androidx.media2.session.LibraryResult.RESULT_ERROR_BAD_VALUE;
import static androidx.media2.session.LibraryResult.RESULT_SUCCESS;
import static androidx.media2.test.common.CommonConstants.MOCK_MEDIA2_LIBRARY_SERVICE;
import static androidx.media2.test.common.MediaBrowserConstants.CUSTOM_ACTION_ASSERT_PARAMS;
import static androidx.media2.test.common.MediaBrowserConstants.LONG_LIST_COUNT;
import static androidx.media2.test.common.MediaBrowserConstants.NOTIFY_CHILDREN_CHANGED_EXTRAS;
import static androidx.media2.test.common.MediaBrowserConstants.NOTIFY_CHILDREN_CHANGED_ITEM_COUNT;
import static androidx.media2.test.common.MediaBrowserConstants.ROOT_EXTRAS;
import static androidx.media2.test.common.MediaBrowserConstants.ROOT_ID;
import static androidx.media2.test.common.MediaBrowserConstants.SUBSCRIBE_ID_NOTIFY_CHILDREN_CHANGED_TO_ALL;
import static androidx.media2.test.common.MediaBrowserConstants.SUBSCRIBE_ID_NOTIFY_CHILDREN_CHANGED_TO_ALL_WITH_NON_SUBSCRIBED_ID;
import static androidx.media2.test.common.MediaBrowserConstants.SUBSCRIBE_ID_NOTIFY_CHILDREN_CHANGED_TO_ONE;
import static androidx.media2.test.common.MediaBrowserConstants.SUBSCRIBE_ID_NOTIFY_CHILDREN_CHANGED_TO_ONE_WITH_NON_SUBSCRIBED_ID;

import static junit.framework.Assert.assertEquals;
import static junit.framework.Assert.assertFalse;
import static junit.framework.Assert.assertNotNull;
import static junit.framework.Assert.assertNull;
import static junit.framework.Assert.assertTrue;
import static junit.framework.Assert.fail;

import static org.junit.Assert.assertNotEquals;

import android.os.Build;
import android.os.Bundle;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.media2.common.MediaItem;
import androidx.media2.common.MediaMetadata;
import androidx.media2.session.LibraryResult;
import androidx.media2.session.MediaBrowser;
import androidx.media2.session.MediaBrowser.BrowserCallback;
import androidx.media2.session.MediaController;
import androidx.media2.session.MediaLibraryService.LibraryParams;
import androidx.media2.session.SessionCommand;
import androidx.media2.session.SessionResult;
import androidx.media2.session.SessionToken;
import androidx.media2.test.client.MediaTestUtils;
import androidx.media2.test.common.MediaBrowserConstants;
import androidx.media2.test.common.TestUtils;
import androidx.test.ext.junit.runners.AndroidJUnit4;
import androidx.test.filters.LargeTest;
import androidx.test.filters.SdkSuppress;
import androidx.versionedparcelable.ParcelUtils;

import org.junit.Test;
import org.junit.runner.RunWith;

import java.util.List;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import java.util.concurrent.atomic.AtomicReference;

/**
 * Tests {@link MediaBrowser.BrowserCallback}.
 * <p>
 * This test inherits {@link MediaControllerCallbackTest} to ensure that inherited APIs from
 * {@link MediaController} works cleanly.
 */
// TODO: (internal cleanup) Move tests that aren't related with callbacks.
@SdkSuppress(minSdkVersion = Build.VERSION_CODES.JELLY_BEAN)
@RunWith(AndroidJUnit4.class)
@LargeTest
public class MediaBrowserCallbackTest extends MediaControllerCallbackTest {
    private static final String TAG = "MediaBrowserCallbackTest";

    @Override
    MediaController onCreateController(@NonNull final SessionToken token,
            @Nullable final Bundle connectionHints, @Nullable final TestBrowserCallback callback)
            throws InterruptedException {
        assertNotNull("Test bug", token);
        final AtomicReference<MediaController> controller = new AtomicReference<>();
        sHandler.postAndSync(new Runnable() {
            @Override
            public void run() {
                // Create controller on the test handler, for changing MediaBrowserCompat's Handler
                // Looper. Otherwise, MediaBrowserCompat will post all the commands to the handler
                // and commands wouldn't be run if tests codes waits on the test handler.
                MediaBrowser.Builder builder = new MediaBrowser.Builder(mContext)
                        .setSessionToken(token)
                        .setControllerCallback(sHandlerExecutor, callback);
                if (connectionHints != null) {
                    builder.setConnectionHints(connectionHints);
                }
                controller.set(builder.build());
            }
        });
        return controller.get();
    }

    final MediaBrowser createBrowser() throws InterruptedException {
        return createBrowser(null, null);
    }

    final MediaBrowser createBrowser(@Nullable Bundle connectionHints,
            @Nullable BrowserCallback callback) throws InterruptedException {
        final SessionToken token = new SessionToken(mContext, MOCK_MEDIA2_LIBRARY_SERVICE);
        return (MediaBrowser) createController(token, true, connectionHints, callback);
    }

    @Test
    public void testGetLibraryRoot() throws Exception {
        prepareLooper();
        final LibraryParams params = new LibraryParams.Builder()
                .setOffline(true).setRecent(true).setExtras(new Bundle()).build();

        MediaBrowser browser = createBrowser();
        setExpectedLibraryParam(browser, params);
        LibraryResult result = browser.getLibraryRoot(params)
                .get(TIMEOUT_MS, TimeUnit.MILLISECONDS);
        assertEquals(RESULT_SUCCESS, result.getResultCode());
        MediaMetadata metadata = result.getMediaItem().getMetadata();
        assertEquals(ROOT_ID, metadata.getString(MediaMetadata.METADATA_KEY_MEDIA_ID));
        assertTrue(TestUtils.equals(ROOT_EXTRAS, result.getLibraryParams().getExtras()));
    }

    @Test
    public void testGetItem() throws Exception {
        prepareLooper();
        final String mediaId = MediaBrowserConstants.MEDIA_ID_GET_ITEM;

        LibraryResult result = createBrowser().getItem(mediaId)
                .get(TIMEOUT_MS, TimeUnit.MILLISECONDS);
        assertEquals(RESULT_SUCCESS, result.getResultCode());
        MediaTestUtils.assertMediaItemHasId(result.getMediaItem(), mediaId);
    }

    @Test
    public void testGetItem_unknownId() throws Exception {
        prepareLooper();
        final String mediaId = "random_media_id";

        LibraryResult result = createBrowser().getItem(mediaId)
                .get(TIMEOUT_MS, TimeUnit.MILLISECONDS);
        assertEquals(RESULT_ERROR_BAD_VALUE, result.getResultCode());
        assertNull(result.getMediaItem());
    }

    @Test
    public void testGetItem_nullResult() throws Exception {
        prepareLooper();
        final String mediaId = MediaBrowserConstants.MEDIA_ID_GET_NULL_ITEM;

        // Exception will be thrown in the service side, and the process will be crashed.
        // In that case one of following will happen
        //   Case 1) Process is crashed. Pending ListenableFuture will get error
        //   Case 2) Due to the frequent crashes with other tests, process may not crash immediately
        //           because the Android shows dialog 'xxx keeps stopping' and defer sending
        //           SIG_KILL until the user's explicit action.
        try {
            LibraryResult result = createBrowser().getItem(mediaId)
                    .get(TIMEOUT_MS, TimeUnit.MILLISECONDS);
            // Case 1.
            assertNotEquals(RESULT_SUCCESS, result.getResultCode());
        } catch (TimeoutException e) {
            // Case 2.
        }
    }

    @Test
    public void testGetItem_invalidResult() throws Exception {
        prepareLooper();
        final String mediaId = MediaBrowserConstants.MEDIA_ID_GET_INVALID_ITEM;

        // Exception will be thrown in the service side, and the process will be crashed.
        // In that case one of following will happen
        //   Case 1) Process is crashed. Pending ListenableFuture will get error
        //   Case 2) Due to the frequent crashes with other tests, process may not crash immediately
        //           because the Android shows dialog 'xxx keeps stopping' and defer sending
        //           SIG_KILL until the user's explicit action.
        try {
            LibraryResult result = createBrowser().getItem(mediaId)
                    .get(TIMEOUT_MS, TimeUnit.MILLISECONDS);
            // Case 1.
            assertNotEquals(RESULT_SUCCESS, result.getResultCode());
        } catch (TimeoutException e) {
            // Case 2.
        }
    }

    @Test
    public void testGetChildren() throws Exception {
        prepareLooper();
        final String parentId = MediaBrowserConstants.PARENT_ID;
        final int page = 4;
        final int pageSize = 10;
        final LibraryParams params = MediaTestUtils.createLibraryParams();

        MediaBrowser browser = createBrowser();
        setExpectedLibraryParam(browser, params);

        LibraryResult result = browser.getChildren(parentId, page, pageSize, params)
                .get(TIMEOUT_MS, TimeUnit.MILLISECONDS);
        assertEquals(RESULT_SUCCESS, result.getResultCode());
        assertNull(result.getLibraryParams());

        MediaTestUtils.assertPaginatedListHasIds(
                result.getMediaItems(), MediaBrowserConstants.GET_CHILDREN_RESULT,
                page, pageSize);
    }

    @Test
    @LargeTest
    public void testGetChildren_withLongList() throws Exception {
        prepareLooper();
        final String parentId = MediaBrowserConstants.PARENT_ID_LONG_LIST;
        final int page = 0;
        final int pageSize = Integer.MAX_VALUE;
        final LibraryParams params = MediaTestUtils.createLibraryParams();

        MediaBrowser browser = createBrowser();
        setExpectedLibraryParam(browser, params);

        LibraryResult result = browser.getChildren(parentId, page, pageSize, params)
                .get(10, TimeUnit.SECONDS);
        assertEquals(RESULT_SUCCESS, result.getResultCode());
        assertNull(result.getLibraryParams());

        List<MediaItem> list = result.getMediaItems();
        assertEquals(LONG_LIST_COUNT, list.size());
        for (int i = 0; i < result.getMediaItems().size(); i++) {
            assertEquals(TestUtils.getMediaIdInDummyList(i), list.get(i).getMediaId());
        }
    }

    @Test
    public void testGetChildren_emptyResult() throws Exception {
        prepareLooper();
        final String parentId = MediaBrowserConstants.PARENT_ID_NO_CHILDREN;

        MediaBrowser browser = createBrowser();
        LibraryResult result = browser.getChildren(parentId, 1, 1, null)
                .get(TIMEOUT_MS, TimeUnit.MILLISECONDS);
        assertEquals(RESULT_SUCCESS, result.getResultCode());
        assertEquals(0, result.getMediaItems().size());
    }

    @Test
    public void testGetChildren_nullResult() throws Exception {
        prepareLooper();
        final String parentId = MediaBrowserConstants.PARENT_ID_ERROR;

        MediaBrowser browser = createBrowser();
        LibraryResult result = browser.getChildren(parentId, 1, 1, null)
                .get(TIMEOUT_MS, TimeUnit.MILLISECONDS);
        assertNotEquals(RESULT_SUCCESS, result.getResultCode());
        assertNull(result.getMediaItems());
    }

    @Test
    public void testSearchCallbacks() throws Exception {
        prepareLooper();
        final String query = MediaBrowserConstants.SEARCH_QUERY;
        final int page = 4;
        final int pageSize = 10;
        final LibraryParams testParams = MediaTestUtils.createLibraryParams();

        final CountDownLatch latchForSearch = new CountDownLatch(1);
        final BrowserCallback callback = new BrowserCallback() {
            @Override
            public void onSearchResultChanged(MediaBrowser browser,
                    String queryOut, int itemCount, LibraryParams params) {
                assertEquals(query, queryOut);
                MediaTestUtils.assertLibraryParamsEquals(testParams, params);
                assertEquals(MediaBrowserConstants.SEARCH_RESULT_COUNT, itemCount);
                latchForSearch.countDown();
            }
        };

        // Request the search.
        MediaBrowser browser = createBrowser(null, callback);
        setExpectedLibraryParam(browser, testParams);
        LibraryResult result = browser.search(query, testParams)
                .get(TIMEOUT_MS, TimeUnit.MILLISECONDS);
        assertEquals(RESULT_SUCCESS, result.getResultCode());

        // Get the search result.
        result = browser.getSearchResult(query, page, pageSize, testParams)
                .get(TIMEOUT_MS, TimeUnit.MILLISECONDS);
        assertEquals(RESULT_SUCCESS, result.getResultCode());
        MediaTestUtils.assertPaginatedListHasIds(result.getMediaItems(),
                MediaBrowserConstants.SEARCH_RESULT, page, pageSize);
    }

    @Test
    @LargeTest
    public void testSearchCallbacks_withLongList() throws Exception {
        prepareLooper();
        final String query = MediaBrowserConstants.SEARCH_QUERY_LONG_LIST;
        final int page = 0;
        final int pageSize = Integer.MAX_VALUE;
        final LibraryParams testParams = MediaTestUtils.createLibraryParams();

        final CountDownLatch latch = new CountDownLatch(1);
        final BrowserCallback callback = new BrowserCallback() {
            @Override
            public void onSearchResultChanged(
                    MediaBrowser browser, String queryOut, int itemCount, LibraryParams params) {
                assertEquals(query, queryOut);
                MediaTestUtils.assertLibraryParamsEquals(testParams, params);
                assertEquals(MediaBrowserConstants.LONG_LIST_COUNT, itemCount);
                latch.countDown();
            }
        };

        MediaBrowser browser = createBrowser(null, callback);
        setExpectedLibraryParam(browser, testParams);
        LibraryResult result = browser.search(query, testParams)
                .get(TIMEOUT_MS, TimeUnit.MILLISECONDS);
        assertEquals(RESULT_SUCCESS, result.getResultCode());

        result = browser.getSearchResult(query, page, pageSize, testParams)
                .get(10, TimeUnit.SECONDS);
        assertEquals(RESULT_SUCCESS, result.getResultCode());
        List<MediaItem> list = result.getMediaItems();
        for (int i = 0; i < list.size(); i++) {
            assertEquals(TestUtils.getMediaIdInDummyList(i), list.get(i).getMediaId());
        }
    }

    @Test
    @LargeTest
    public void testOnSearchResultChanged_searchTakesTime() throws Exception {
        prepareLooper();
        final String query = MediaBrowserConstants.SEARCH_QUERY_TAKES_TIME;
        final LibraryParams testParams = MediaTestUtils.createLibraryParams();

        final CountDownLatch latch = new CountDownLatch(1);
        final BrowserCallback callback = new BrowserCallback() {
            @Override
            public void onSearchResultChanged(
                    MediaBrowser browser, String queryOut, int itemCount, LibraryParams params) {
                assertEquals(query, queryOut);
                MediaTestUtils.assertLibraryParamsEquals(testParams, params);
                assertEquals(MediaBrowserConstants.SEARCH_RESULT_COUNT, itemCount);
                latch.countDown();
            }
        };

        MediaBrowser browser = createBrowser(null, callback);
        setExpectedLibraryParam(browser, testParams);
        LibraryResult result = browser.search(query, testParams)
                .get(MediaBrowserConstants.SEARCH_TIME_IN_MS + TIMEOUT_MS,
                        TimeUnit.MILLISECONDS);
        assertEquals(RESULT_SUCCESS, result.getResultCode());
    }

    @Test
    public void testOnSearchResultChanged_emptyResult() throws Exception {
        prepareLooper();
        final String query = MediaBrowserConstants.SEARCH_QUERY_EMPTY_RESULT;
        final LibraryParams testParams = MediaTestUtils.createLibraryParams();

        final CountDownLatch latch = new CountDownLatch(1);
        final BrowserCallback callback = new BrowserCallback() {
            @Override
            public void onSearchResultChanged(
                    MediaBrowser browser, String queryOut, int itemCount, LibraryParams params) {
                assertEquals(query, queryOut);
                MediaTestUtils.assertLibraryParamsEquals(testParams, params);
                assertEquals(0, itemCount);
                latch.countDown();
            }
        };

        MediaBrowser browser = createBrowser(null, callback);
        setExpectedLibraryParam(browser, testParams);
        LibraryResult result = browser.search(query, testParams)
                .get(TIMEOUT_MS, TimeUnit.MILLISECONDS);
        assertEquals(RESULT_SUCCESS, result.getResultCode());
    }

    @Test
    public void testOnChildrenChanged_calledWhenSubscribed() throws Exception {
        // This test uses MediaLibrarySession.notifyChildrenChanged().
        prepareLooper();
        final String expectedParentId = SUBSCRIBE_ID_NOTIFY_CHILDREN_CHANGED_TO_ALL;

        final CountDownLatch latch = new CountDownLatch(1);
        final BrowserCallback controllerCallbackProxy = new BrowserCallback() {
            @Override
            public void onChildrenChanged(MediaBrowser browser, String parentId,
                    int itemCount, LibraryParams params) {
                assertEquals(expectedParentId, parentId);
                assertEquals(NOTIFY_CHILDREN_CHANGED_ITEM_COUNT, itemCount);
                MediaTestUtils.assertLibraryParamsEquals(params, NOTIFY_CHILDREN_CHANGED_EXTRAS);
                latch.countDown();
            }
        };

        LibraryResult result = createBrowser(null, controllerCallbackProxy)
                .subscribe(expectedParentId, null)
                .get(TIMEOUT_MS, TimeUnit.MILLISECONDS);
        assertEquals(RESULT_SUCCESS, result.getResultCode());

        // The MediaLibrarySession in MockMediaLibraryService is supposed to call
        // notifyChildrenChanged() in its callback onSubscribe().
        assertTrue(latch.await(TIMEOUT_MS, TimeUnit.MILLISECONDS));
    }

    @Test
    public void testOnChildrenChanged_calledWhenSubscribed2() throws Exception {
        // This test uses MediaLibrarySession.notifyChildrenChanged(ControllerInfo).
        prepareLooper();
        final String expectedParentId = SUBSCRIBE_ID_NOTIFY_CHILDREN_CHANGED_TO_ONE;

        final CountDownLatch latch = new CountDownLatch(1);
        final BrowserCallback controllerCallbackProxy = new BrowserCallback() {
            @Override
            public void onChildrenChanged(MediaBrowser browser, String parentId,
                    int itemCount, LibraryParams params) {
                assertEquals(expectedParentId, parentId);
                assertEquals(NOTIFY_CHILDREN_CHANGED_ITEM_COUNT, itemCount);
                MediaTestUtils.assertLibraryParamsEquals(params, NOTIFY_CHILDREN_CHANGED_EXTRAS);
                latch.countDown();
            }
        };

        LibraryResult result = createBrowser(null, controllerCallbackProxy)
                .subscribe(expectedParentId, null)
                .get(TIMEOUT_MS, TimeUnit.MILLISECONDS);
        assertEquals(RESULT_SUCCESS, result.getResultCode());

        // The MediaLibrarySession in MockMediaLibraryService is supposed to call
        // notifyChildrenChanged(ControllerInfo) in its callback onSubscribe().
        assertTrue(latch.await(TIMEOUT_MS, TimeUnit.MILLISECONDS));
    }

    @Test
    public void testOnChildrenChanged_notCalledWhenNotSubscribed() throws Exception {
        // This test uses MediaLibrarySession.notifyChildrenChanged().
        prepareLooper();
        final String subscribedMediaId =
                SUBSCRIBE_ID_NOTIFY_CHILDREN_CHANGED_TO_ALL_WITH_NON_SUBSCRIBED_ID;
        final CountDownLatch latch = new CountDownLatch(1);

        final BrowserCallback controllerCallbackProxy = new BrowserCallback() {
            @Override
            public void onChildrenChanged(MediaBrowser browser, String parentId,
                    int itemCount, LibraryParams params) {
                // Unexpected call.
                fail();
                latch.countDown();
            }
        };

        LibraryResult result = createBrowser(null, controllerCallbackProxy)
                .subscribe(subscribedMediaId, null)
                .get(TIMEOUT_MS, TimeUnit.MILLISECONDS);
        assertEquals(RESULT_SUCCESS, result.getResultCode());

        // The MediaLibrarySession in MockMediaLibraryService is supposed to call
        // notifyChildrenChanged() in its callback onSubscribe(), but with a different media ID.
        // Therefore, onChildrenChanged() should not be called.
        assertFalse(latch.await(TIMEOUT_MS, TimeUnit.MILLISECONDS));
    }

    @Test
    public void testOnChildrenChanged_notCalledWhenNotSubscribed2() throws Exception {
        // This test uses MediaLibrarySession.notifyChildrenChanged(ControllerInfo).
        prepareLooper();
        final String subscribedMediaId =
                SUBSCRIBE_ID_NOTIFY_CHILDREN_CHANGED_TO_ONE_WITH_NON_SUBSCRIBED_ID;
        final CountDownLatch latch = new CountDownLatch(1);

        final BrowserCallback controllerCallbackProxy = new BrowserCallback() {
            @Override
            public void onChildrenChanged(MediaBrowser browser, String parentId,
                    int itemCount, LibraryParams params) {
                // Unexpected call.
                fail();
                latch.countDown();
            }
        };

        LibraryResult result = createBrowser(null, controllerCallbackProxy)
                .subscribe(subscribedMediaId, null)
                .get(TIMEOUT_MS, TimeUnit.MILLISECONDS);
        assertEquals(RESULT_SUCCESS, result.getResultCode());

        // The MediaLibrarySession in MockMediaLibraryService is supposed to call
        // notifyChildrenChanged(ControllerInfo) in its callback onSubscribe(),
        // but with a different media ID.
        // Therefore, onChildrenChanged() should not be called.
        assertFalse(latch.await(TIMEOUT_MS, TimeUnit.MILLISECONDS));
    }

    private void setExpectedLibraryParam(MediaBrowser browser, LibraryParams params)
            throws Exception {
        SessionCommand command = new SessionCommand(CUSTOM_ACTION_ASSERT_PARAMS, null);
        Bundle args = new Bundle();
        ParcelUtils.putVersionedParcelable(args, CUSTOM_ACTION_ASSERT_PARAMS, params);
        SessionResult result = browser.sendCustomCommand(command, args)
                .get(TIMEOUT_MS, TimeUnit.MILLISECONDS);
        assertEquals(SessionResult.RESULT_SUCCESS, result.getResultCode());
    }
}