Refactor CaptionAppearanceFragment to improve maintainability (1/n)

Root cause: There is a bunch of different logic of preferences in CaptionAppearanceFragment. It’s hard to implement new features and hard to maintain and hard to be testable.
Solution: Move out preview preference logic of CaptionAppearanceFragment into controllers to reduce the complexity of the relationship between preference and fragment.

Bug: 197695932
Test: make RunSettingsRoboTests ROBOTEST_FILTER=com.android.settings.accessibility
Change-Id: Ie8acdcb8659606ce3faf6d5532cc73ee19024725

res/xml/captioning_appearance.xml

@@ -25,7 +25,8 @@
         android:title="@string/summary_placeholder"
         android:layout="@layout/captioning_preview"
         android:selectable="false"
-        settings:searchable="false"/>
+        settings:searchable="false"
+        settings:controller="com.android.settings.accessibility.CaptionPreviewPreferenceController"/>
 
     <ListPreference
         android:entries="@array/captioning_font_size_selector_titles"

src/com/android/settings/accessibility/CaptionAppearanceFragment.java

@@ -24,10 +24,7 @@ import android.content.Context;
 import android.content.res.Resources;
 import android.graphics.Color;
 import android.os.Bundle;
-import android.os.Handler;
-import android.os.Looper;
 import android.provider.Settings;
-import android.view.View;
 import android.view.accessibility.CaptioningManager;
 
 import androidx.preference.ListPreference;
@@ -35,18 +32,14 @@ import androidx.preference.Preference;
 import androidx.preference.Preference.OnPreferenceChangeListener;
 import androidx.preference.PreferenceCategory;
 
-import com.android.internal.widget.SubtitleView;
 import com.android.settings.R;
 import com.android.settings.accessibility.ListDialogPreference.OnValueChangedListener;
 import com.android.settings.dashboard.DashboardFragment;
 import com.android.settings.search.BaseSearchIndexProvider;
-import com.android.settingslib.accessibility.AccessibilityUtils;
 import com.android.settingslib.search.SearchIndexable;
-import com.android.settingslib.widget.LayoutPreference;
 
 import java.util.ArrayList;
 import java.util.List;
-import java.util.Locale;
 
 /** Settings fragment containing font style of captioning properties. */
 @SearchIndexable(forTarget = SearchIndexable.ALL & ~SearchIndexable.ARC)
@@ -54,7 +47,6 @@ public class CaptionAppearanceFragment extends DashboardFragment
         implements OnPreferenceChangeListener, OnValueChangedListener {
 
     private static final String TAG = "CaptionAppearanceFragment";
-    private static final String PREF_CAPTION_PREVIEW = "caption_preview";
     private static final String PREF_BACKGROUND_COLOR = "captioning_background_color";
     private static final String PREF_BACKGROUND_OPACITY = "captioning_background_opacity";
     private static final String PREF_FOREGROUND_COLOR = "captioning_foreground_color";
@@ -68,13 +60,7 @@ public class CaptionAppearanceFragment extends DashboardFragment
     private static final String PREF_PRESET = "captioning_preset";
     private static final String PREF_CUSTOM = "custom";
 
-    /* WebVtt specifies line height as 5.3% of the viewport height. */
-    private static final float LINE_HEIGHT_RATIO = 0.0533f;
-
     private CaptioningManager mCaptioningManager;
-    private SubtitleView mPreviewText;
-    private View mPreviewWindow;
-    private View mPreviewViewport;
 
     // Standard options.
     private ListPreference mFontSize;
@@ -96,18 +82,6 @@ public class CaptionAppearanceFragment extends DashboardFragment
 
     private final List<Preference> mPreferenceList = new ArrayList<>();
 
-    private final Handler mHandler = new Handler(Looper.getMainLooper());
-    private final View.OnLayoutChangeListener mLayoutChangeListener =
-            new View.OnLayoutChangeListener() {
-                @Override
-                public void onLayoutChange(View v, int left, int top, int right, int bottom,
-                        int oldLeft, int oldTop, int oldRight, int oldBottom) {
-                    // Remove the listener once the callback is triggered.
-                    mPreviewViewport.removeOnLayoutChangeListener(this);
-                    mHandler.post(() ->refreshPreviewText());
-                }
-            };
-
     @Override
     public int getMetricsCategory() {
         return SettingsEnums.ACCESSIBILITY_CAPTION_APPEARANCE;
@@ -123,7 +97,6 @@ public class CaptionAppearanceFragment extends DashboardFragment
         updateAllPreferences();
         refreshShowingCustom();
         installUpdateListeners();
-        refreshPreviewText();
     }
 
     @Override
@@ -136,83 +109,7 @@ public class CaptionAppearanceFragment extends DashboardFragment
         return TAG;
     }
 
-    private void refreshPreviewText() {
-        final Context context = getActivity();
-        if (context == null) {
-            // We've been destroyed, abort!
-            return;
-        }
-
-        final SubtitleView preview = mPreviewText;
-        if (preview != null) {
-            final int styleId = mCaptioningManager.getRawUserStyle();
-            applyCaptionProperties(mCaptioningManager, preview, mPreviewViewport, styleId);
-
-            final Locale locale = mCaptioningManager.getLocale();
-            if (locale != null) {
-                final CharSequence localizedText = AccessibilityUtils.getTextForLocale(
-                        context, locale, R.string.captioning_preview_text);
-                preview.setText(localizedText);
-            } else {
-                preview.setText(R.string.captioning_preview_text);
-            }
-
-            final CaptioningManager.CaptionStyle style = mCaptioningManager.getUserStyle();
-            if (style.hasWindowColor()) {
-                mPreviewWindow.setBackgroundColor(style.windowColor);
-            } else {
-                final CaptioningManager.CaptionStyle defStyle =
-                        CaptioningManager.CaptionStyle.DEFAULT;
-                mPreviewWindow.setBackgroundColor(defStyle.windowColor);
-            }
-        }
-    }
-
-    /**
-     * Updates font style of captioning properties for preview screen.
-     *
-     * @param manager caption manager
-     * @param previewText preview text
-     * @param previewWindow preview window
-     * @param styleId font style id
-     */
-    public static void applyCaptionProperties(CaptioningManager manager, SubtitleView previewText,
-            View previewWindow, int styleId) {
-        previewText.setStyle(styleId);
-
-        final Context context = previewText.getContext();
-        final ContentResolver cr = context.getContentResolver();
-        final float fontScale = manager.getFontScale();
-        if (previewWindow != null) {
-            // Assume the viewport is clipped with a 16:9 aspect ratio.
-            final float virtualHeight = Math.max(9 * previewWindow.getWidth(),
-                    16 * previewWindow.getHeight()) / 16.0f;
-            previewText.setTextSize(virtualHeight * LINE_HEIGHT_RATIO * fontScale);
-        } else {
-            final float textSize = context.getResources().getDimension(
-                    R.dimen.caption_preview_text_size);
-            previewText.setTextSize(textSize * fontScale);
-        }
-
-        final Locale locale = manager.getLocale();
-        if (locale != null) {
-            final CharSequence localizedText = AccessibilityUtils.getTextForLocale(
-                    context, locale, R.string.captioning_preview_characters);
-            previewText.setText(localizedText);
-        } else {
-            previewText.setText(R.string.captioning_preview_characters);
-        }
-    }
-
     private void initializeAllPreferences() {
-        final LayoutPreference captionPreview = findPreference(PREF_CAPTION_PREVIEW);
-
-        mPreviewText = captionPreview.findViewById(R.id.preview_text);
-
-        mPreviewWindow = captionPreview.findViewById(R.id.preview_window);
-
-        mPreviewViewport = captionPreview.findViewById(R.id.preview_viewport);
-        mPreviewViewport.addOnLayoutChangeListener(mLayoutChangeListener);
 
         final Resources res = getResources();
         final int[] presetValues = res.getIntArray(R.array.captioning_preset_selector_values);
@@ -400,8 +297,6 @@ public class CaptionAppearanceFragment extends DashboardFragment
         } else if (mEdgeType == preference) {
             Settings.Secure.putInt(cr, Settings.Secure.ACCESSIBILITY_CAPTIONING_EDGE_TYPE, value);
         }
-
-        refreshPreviewText();
         enableCaptioningManager();
     }
 
@@ -411,13 +306,11 @@ public class CaptionAppearanceFragment extends DashboardFragment
         if (mTypeface == preference) {
             Settings.Secure.putString(
                     cr, Settings.Secure.ACCESSIBILITY_CAPTIONING_TYPEFACE, (String) value);
-            refreshPreviewText();
             enableCaptioningManager();
         } else if (mFontSize == preference) {
             Settings.Secure.putFloat(
                     cr, Settings.Secure.ACCESSIBILITY_CAPTIONING_FONT_SCALE,
                     Float.parseFloat((String) value));
-            refreshPreviewText();
             enableCaptioningManager();
         }
 

src/com/android/settings/accessibility/CaptionHelper.java

@@ -0,0 +1,80 @@
+/*
+ * Copyright (C) 2022 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 com.android.settings.accessibility;
+
+import android.content.Context;
+import android.view.View;
+import android.view.accessibility.CaptioningManager;
+
+import com.android.internal.widget.SubtitleView;
+import com.android.settings.R;
+import com.android.settingslib.accessibility.AccessibilityUtils;
+
+import com.google.common.annotations.VisibleForTesting;
+
+import java.util.Locale;
+
+/**
+ * Helper class for caption.
+ */
+public class CaptionHelper {
+
+    /* WebVtt specifies line height as 5.3% of the viewport height. */
+    @VisibleForTesting
+    static final float LINE_HEIGHT_RATIO = 0.0533f;
+
+    private final Context mContext;
+    private final CaptioningManager mCaptioningManager;
+
+    public CaptionHelper(Context context) {
+        mContext = context;
+        mCaptioningManager = context.getSystemService(CaptioningManager.class);
+    }
+
+    /**
+     * Updates font style of captioning properties for preview screen.
+     *
+     * @param previewText preview text
+     * @param previewWindow preview window
+     * @param styleId font style id
+     */
+    public void applyCaptionProperties(SubtitleView previewText, View previewWindow,
+            int styleId) {
+        previewText.setStyle(styleId);
+
+        final float fontScale = mCaptioningManager.getFontScale();
+        if (previewWindow != null) {
+            // Assume the viewport is clipped with a 16:9 aspect ratio.
+            final float virtualHeight = Math.max(9 * previewWindow.getWidth(),
+                    16 * previewWindow.getHeight()) / 16.0f;
+            previewText.setTextSize(virtualHeight * LINE_HEIGHT_RATIO * fontScale);
+        } else {
+            final float textSize = mContext.getResources().getDimension(
+                    R.dimen.caption_preview_text_size);
+            previewText.setTextSize(textSize * fontScale);
+        }
+
+        final Locale locale = mCaptioningManager.getLocale();
+        if (locale != null) {
+            final CharSequence localizedText = AccessibilityUtils.getTextForLocale(
+                    mContext, locale, R.string.captioning_preview_characters);
+            previewText.setText(localizedText);
+        } else {
+            previewText.setText(R.string.captioning_preview_characters);
+        }
+    }
+}

src/com/android/settings/accessibility/CaptionPreviewPreferenceController.java

@@ -0,0 +1,135 @@
+/*
+ * Copyright (C) 2022 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 com.android.settings.accessibility;
+
+import android.content.Context;
+import android.os.Handler;
+import android.os.Looper;
+import android.provider.Settings;
+import android.view.View;
+import android.view.accessibility.CaptioningManager;
+
+import androidx.annotation.VisibleForTesting;
+import androidx.preference.PreferenceScreen;
+
+import com.android.internal.widget.SubtitleView;
+import com.android.settings.R;
+import com.android.settings.core.BasePreferenceController;
+import com.android.settingslib.accessibility.AccessibilityUtils;
+import com.android.settingslib.core.lifecycle.LifecycleObserver;
+import com.android.settingslib.core.lifecycle.events.OnStart;
+import com.android.settingslib.core.lifecycle.events.OnStop;
+import com.android.settingslib.widget.LayoutPreference;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.Locale;
+
+/** Controller that shows the caption locale summary. */
+public class CaptionPreviewPreferenceController extends BasePreferenceController
+        implements LifecycleObserver, OnStart, OnStop {
+
+    @VisibleForTesting
+    static final List<String> CAPTIONING_FEATURE_KEYS = Arrays.asList(
+            Settings.Secure.ACCESSIBILITY_CAPTIONING_FOREGROUND_COLOR,
+            Settings.Secure.ACCESSIBILITY_CAPTIONING_BACKGROUND_COLOR,
+            Settings.Secure.ACCESSIBILITY_CAPTIONING_WINDOW_COLOR,
+            Settings.Secure.ACCESSIBILITY_CAPTIONING_EDGE_COLOR,
+            Settings.Secure.ACCESSIBILITY_CAPTIONING_PRESET,
+            Settings.Secure.ACCESSIBILITY_CAPTIONING_EDGE_TYPE,
+            Settings.Secure.ACCESSIBILITY_CAPTIONING_TYPEFACE,
+            Settings.Secure.ACCESSIBILITY_CAPTIONING_FONT_SCALE
+    );
+    private final Handler mHandler = new Handler(Looper.getMainLooper());
+    @VisibleForTesting
+    AccessibilitySettingsContentObserver mSettingsContentObserver;
+    private CaptioningManager mCaptioningManager;
+    private CaptionHelper mCaptionHelper;
+    private LayoutPreference mPreference;
+    private SubtitleView mPreviewText;
+    private View mPreviewWindow;
+    private View mPreviewViewport;
+
+    public CaptionPreviewPreferenceController(Context context, String preferenceKey) {
+        super(context, preferenceKey);
+        mCaptioningManager = context.getSystemService(CaptioningManager.class);
+        mCaptionHelper = new CaptionHelper(context);
+        mSettingsContentObserver = new AccessibilitySettingsContentObserver(mHandler);
+        mSettingsContentObserver.registerKeysToObserverCallback(CAPTIONING_FEATURE_KEYS,
+                key -> refreshPreviewText());
+    }
+
+    @Override
+    public void onStart() {
+        mSettingsContentObserver.register(mContext.getContentResolver());
+    }
+
+    @Override
+    public void onStop() {
+        mContext.getContentResolver().unregisterContentObserver(mSettingsContentObserver);
+    }
+
+    @Override
+    public int getAvailabilityStatus() {
+        return AVAILABLE;
+    }
+
+    @Override
+    public void displayPreference(PreferenceScreen screen) {
+        super.displayPreference(screen);
+        mPreference = screen.findPreference(getPreferenceKey());
+        mPreviewText = mPreference.findViewById(R.id.preview_text);
+        mPreviewWindow = mPreference.findViewById(R.id.preview_window);
+        mPreviewViewport = mPreference.findViewById(R.id.preview_viewport);
+        mPreviewViewport.addOnLayoutChangeListener(new View.OnLayoutChangeListener() {
+            @Override
+            public void onLayoutChange(View v, int left, int top, int right,
+                    int bottom, int oldLeft, int oldTop, int oldRight, int oldBottom) {
+                if ((oldRight - oldLeft) != (right - left)) {
+                    // Remove the listener once the callback is triggered.
+                    mPreviewViewport.removeOnLayoutChangeListener(this);
+                    mHandler.post(() -> refreshPreviewText());
+                }
+            }
+        });
+    }
+
+    private void refreshPreviewText() {
+        if (mPreviewText != null) {
+            final int styleId = mCaptioningManager.getRawUserStyle();
+            mCaptionHelper.applyCaptionProperties(mPreviewText, mPreviewViewport, styleId);
+
+            final Locale locale = mCaptioningManager.getLocale();
+            if (locale != null) {
+                final CharSequence localizedText = AccessibilityUtils.getTextForLocale(
+                        mContext, locale, R.string.captioning_preview_text);
+                mPreviewText.setText(localizedText);
+            } else {
+                mPreviewText.setText(R.string.captioning_preview_text);
+            }
+
+            final CaptioningManager.CaptionStyle style = mCaptioningManager.getUserStyle();
+            if (style.hasWindowColor()) {
+                mPreviewWindow.setBackgroundColor(style.windowColor);
+            } else {
+                final CaptioningManager.CaptionStyle defStyle =
+                        CaptioningManager.CaptionStyle.DEFAULT;
+                mPreviewWindow.setBackgroundColor(defStyle.windowColor);
+            }
+        }
+    }
+}

src/com/android/settings/accessibility/PresetPreference.java

@@ -19,26 +19,24 @@ package com.android.settings.accessibility;
 import android.content.Context;
 import android.util.AttributeSet;
 import android.view.View;
-import android.view.accessibility.CaptioningManager;
 import android.view.accessibility.CaptioningManager.CaptionStyle;
 import android.widget.TextView;
 
 import com.android.internal.widget.SubtitleView;
 import com.android.settings.R;
 
+/** Grid preference that allows the user to pick a captioning preset type. */
 public class PresetPreference extends ListDialogPreference {
-    private static final float DEFAULT_FONT_SIZE = 32f;
 
-    private final CaptioningManager mCaptioningManager;
+    private static final float DEFAULT_FONT_SIZE = 32f;
+    private final CaptionHelper mCaptionHelper;
 
     public PresetPreference(Context context, AttributeSet attrs) {
         super(context, attrs);
+        mCaptionHelper = new CaptionHelper(context);
 
         setDialogLayoutResource(R.layout.grid_picker_dialog);
         setListItemLayoutResource(R.layout.preset_picker_item);
-
-        mCaptioningManager = (CaptioningManager) context.getSystemService(
-                Context.CAPTIONING_SERVICE);
     }
 
     @Override
@@ -50,17 +48,16 @@ public class PresetPreference extends ListDialogPreference {
     @Override
     protected void onBindListItem(View view, int index) {
         final View previewViewport = view.findViewById(R.id.preview_viewport);
-        final SubtitleView previewText = (SubtitleView) view.findViewById(R.id.preview);
+        final SubtitleView previewText = view.findViewById(R.id.preview);
         final int value = getValueAt(index);
-        CaptionAppearanceFragment.applyCaptionProperties(
+        mCaptionHelper.applyCaptionProperties(previewText, previewViewport, value);
-                mCaptioningManager, previewText, previewViewport, value);
 
         final float density = getContext().getResources().getDisplayMetrics().density;
         previewText.setTextSize(DEFAULT_FONT_SIZE * density);
 
         final CharSequence title = getTitleAt(index);
         if (title != null) {
-            final TextView summary = (TextView) view.findViewById(R.id.summary);
+            final TextView summary = view.findViewById(R.id.summary);
             summary.setText(title);
         }
     }

tests/robotests/src/com/android/settings/accessibility/CaptionHelperTest.java

@@ -0,0 +1,104 @@
+/*
+ * Copyright (C) 2022 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 com.android.settings.accessibility;
+
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+import android.content.Context;
+import android.view.View;
+import android.view.accessibility.CaptioningManager;
+
+import androidx.test.core.app.ApplicationProvider;
+
+import com.android.internal.widget.SubtitleView;
+import com.android.settings.R;
+
+import org.junit.Before;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mockito.Mock;
+import org.mockito.Spy;
+import org.mockito.junit.MockitoJUnit;
+import org.mockito.junit.MockitoRule;
+import org.robolectric.RobolectricTestRunner;
+
+import java.util.Locale;
+
+/** Tests for {@link CaptionHelper}. */
+@RunWith(RobolectricTestRunner.class)
+public class CaptionHelperTest {
+
+    @Rule
+    public final MockitoRule mMockitoRule = MockitoJUnit.rule();
+    @Mock
+    private CaptioningManager mCaptioningManager;
+    @Mock
+    private SubtitleView mSubtitleView;
+    @Mock
+    private View mPreviewWindow;
+    @Spy
+    private final Context mContext = ApplicationProvider.getApplicationContext();
+    private CaptionHelper mCaptionHelper;
+
+    @Before
+    public void setUp() {
+        when(mContext.getSystemService(CaptioningManager.class)).thenReturn(mCaptioningManager);
+        mCaptionHelper = new CaptionHelper(mContext);
+    }
+
+    @Test
+    public void applyCaptionProperties_verifyAction() {
+        final float fontScale = 1.0f;
+        when(mCaptioningManager.getFontScale()).thenReturn(fontScale);
+        final int windowSize = 100;
+        when(mPreviewWindow.getWidth()).thenReturn(windowSize);
+        when(mPreviewWindow.getHeight()).thenReturn(windowSize);
+        final float textSize = CaptionHelper.LINE_HEIGHT_RATIO * windowSize * fontScale;
+
+        mCaptionHelper.applyCaptionProperties(mSubtitleView, mPreviewWindow, /* styleId= */ 0);
+
+        verify(mSubtitleView).setTextSize(textSize);
+        verify(mSubtitleView).setText(R.string.captioning_preview_characters);
+    }
+
+    @Test
+    public void applyCaptionProperties_withoutPreviewWindow_verifyAction() {
+        final float fontScale = 1.0f;
+        when(mCaptioningManager.getFontScale()).thenReturn(fontScale);
+        final float textSize = mContext.getResources().getDimension(
+                R.dimen.caption_preview_text_size) * fontScale;
+
+        mCaptionHelper.applyCaptionProperties(mSubtitleView, /* PreviewWindow= */ null,
+                /* styleId= */ 0);
+
+        verify(mSubtitleView).setTextSize(textSize);
+        verify(mSubtitleView).setText(R.string.captioning_preview_characters);
+    }
+
+    @Test
+    public void applyCaptionProperties_localeUS_verifyAction() {
+        when(mCaptioningManager.getLocale()).thenReturn(Locale.US);
+        final String text = mContext.getString(R.string.captioning_preview_characters);
+
+        mCaptionHelper.applyCaptionProperties(mSubtitleView, /* PreviewWindow= */ null,
+                /* styleId= */ 0);
+
+        verify(mSubtitleView).setText(text);
+    }
+}

tests/robotests/src/com/android/settings/accessibility/CaptionPreviewPreferenceControllerTest.java

@@ -0,0 +1,92 @@
+/*
+ * Copyright (C) 2022 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 com.android.settings.accessibility;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+import android.content.ContentResolver;
+import android.content.Context;
+import android.provider.Settings;
+import android.view.View;
+
+import androidx.preference.PreferenceScreen;
+import androidx.test.core.app.ApplicationProvider;
+
+import com.android.settings.core.BasePreferenceController;
+import com.android.settingslib.widget.LayoutPreference;
+
+import org.junit.Before;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mockito.Mock;
+import org.mockito.Spy;
+import org.mockito.junit.MockitoJUnit;
+import org.mockito.junit.MockitoRule;
+import org.robolectric.RobolectricTestRunner;
+
+/** Tests for {@link CaptionPreviewPreferenceController}. */
+@RunWith(RobolectricTestRunner.class)
+public class CaptionPreviewPreferenceControllerTest {
+
+    @Rule
+    public final MockitoRule mMockitoRule = MockitoJUnit.rule();
+    @Mock
+    private PreferenceScreen mScreen;
+    @Mock
+    private ContentResolver mContentResolver;
+    @Spy
+    private final Context mContext = ApplicationProvider.getApplicationContext();
+    private CaptionPreviewPreferenceController mController;
+    private LayoutPreference mLayoutPreference;
+
+    @Before
+    public void setUp() {
+        when(mContext.getContentResolver()).thenReturn(mContentResolver);
+        mController = new CaptionPreviewPreferenceController(mContext,
+                "captioning_preference_switch");
+        final View view = new View(mContext);
+        mLayoutPreference = new LayoutPreference(mContext, view);
+        when(mScreen.findPreference(mController.getPreferenceKey())).thenReturn(mLayoutPreference);
+    }
+
+    @Test
+    public void getAvailabilityStatus_shouldReturnAvailable() {
+        assertThat(mController.getAvailabilityStatus())
+                .isEqualTo(BasePreferenceController.AVAILABLE);
+    }
+
+    @Test
+    public void onStart_registerSpecificContentObserverForSpecificKeys() {
+        mController.onStart();
+
+        for (String key : mController.CAPTIONING_FEATURE_KEYS) {
+            verify(mContentResolver).registerContentObserver(Settings.Secure.getUriFor(key),
+                    /* notifyForDescendants= */ false, mController.mSettingsContentObserver);
+        }
+    }
+
+    @Test
+    public void onPause_unregisterContentObserver() {
+        mController.onStop();
+
+        verify(mContentResolver).unregisterContentObserver(mController.mSettingsContentObserver);
+    }
+}