[Android NTP] Reduce API surface of NewTabPageAdapter.

Remove:
* getSignInPromoPosition()
* getSuggestionPosition()

Change to default visibility:
* getBottomSpacerPosition()
* getLastContentItemPosition()

Change to private:
* hasAllBeenDismissed()
* getSuggestionsSection()
* getChildPositionOffset()

Two methods are added for tests:
* getSectionForTesting()
* getRootForTesting()

BUG=616090

Review-Url: https://codereview.chromium.org/2532953002
Cr-Commit-Position: refs/heads/master@{#436327}

chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/NewTabPageAdapter.java

@@ -32,7 +32,6 @@ import org.chromium.chrome.browser.ntp.snippets.SuggestionsSource;
 import org.chromium.chrome.browser.offlinepages.OfflinePageBridge;
 
 import java.util.ArrayList;
-import java.util.Collections;
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
@@ -118,10 +117,10 @@ public class NewTabPageAdapter
 
             // We use our own implementation of the dismissal animation, so we don't call the
             // parent implementation. (by default it changes the translation-X and elevation)
-            mRecyclerView.updateViewStateForDismiss(dX, viewHolder);
+            mRecyclerView.updateViewStateForDismiss(dX, (NewTabPageViewHolder) viewHolder);
 
             // If there is another item that should be animated at the same time, do the same to it.
-            ViewHolder siblingViewHolder = getDismissSibling(viewHolder);
+            NewTabPageViewHolder siblingViewHolder = getDismissSibling(viewHolder);
             if (siblingViewHolder != null) {
                 mRecyclerView.updateViewStateForDismiss(dX, siblingViewHolder);
             }
@@ -388,26 +387,14 @@ public class NewTabPageAdapter
         return RecyclerView.NO_POSITION;
     }
 
-    public int getSignInPromoPosition() {
-        return getChildPositionOffset(mSigninPromo);
-    }
-
-    public int getBottomSpacerPosition() {
+    int getBottomSpacerPosition() {
         return getChildPositionOffset(mBottomSpacer);
     }
 
-    public int getLastContentItemPosition() {
+    int getLastContentItemPosition() {
         return getChildPositionOffset(hasAllBeenDismissed() ? mAllDismissed : mFooter);
     }
 
-    public int getSuggestionPosition(SnippetArticle article) {
-        for (int i = 0; i < mRoot.getItemCount(); i++) {
-            SnippetArticle articleToCheck = mRoot.getSuggestionAt(i);
-            if (articleToCheck != null && articleToCheck.equals(article)) return i;
-        }
-        return RecyclerView.NO_POSITION;
-    }
-
     private void setSuggestions(@CategoryInt int category, List<SnippetArticle> suggestions,
             @CategoryStatusEnum int status) {
         // Count the number of suggestions before this category.
@@ -560,24 +547,16 @@ public class NewTabPageAdapter
     /**
      * Returns another view holder that should be dismissed at the same time as the provided one.
      */
-    public ViewHolder getDismissSibling(ViewHolder viewHolder) {
+    public NewTabPageViewHolder getDismissSibling(ViewHolder viewHolder) {
         int swipePos = viewHolder.getAdapterPosition();
         int siblingPosDelta = mRoot.getDismissSiblingPosDelta(swipePos);
         if (siblingPosDelta == 0) return null;
 
-        return mRecyclerView.findViewHolderForAdapterPosition(siblingPosDelta + swipePos);
+        return (NewTabPageViewHolder) mRecyclerView.findViewHolderForAdapterPosition(
+                siblingPosDelta + swipePos);
     }
 
-    /**
-     * @return The info associated to the provided category.
-     * @throws NullPointerException if {@code category} isn't currently registered with the adapter.
-     * */
-    public SuggestionsCategoryInfo getCategoryInfo(@CategoryInt int category) {
-        return mSections.get(category).getCategoryInfo();
-    }
-
-    @VisibleForTesting
-    public boolean hasAllBeenDismissed() {
+    private boolean hasAllBeenDismissed() {
         return mSections.isEmpty() && !mSigninPromo.isVisible();
     }
 
@@ -601,20 +580,13 @@ public class NewTabPageAdapter
      * @return Returns the {@link SuggestionsSection} that contains the item at
      *     {@code itemPosition}, or null if the item is not part of one.
      */
-    @VisibleForTesting
-    SuggestionsSection getSuggestionsSection(int itemPosition) {
+    private SuggestionsSection getSuggestionsSection(int itemPosition) {
         TreeNode child = mRoot.getChildForPosition(itemPosition);
         if (!(child instanceof SuggestionsSection)) return null;
         return (SuggestionsSection) child;
     }
 
-    @VisibleForTesting
-    List<TreeNode> getChildren() {
-        return Collections.unmodifiableList(mChildren);
-    }
-
-    @VisibleForTesting
-    int getChildPositionOffset(TreeNode child) {
+    private int getChildPositionOffset(TreeNode child) {
         return mRoot.getStartingOffsetForChild(child);
     }
 
@@ -632,12 +604,20 @@ public class NewTabPageAdapter
         return RecyclerView.NO_POSITION;
     }
 
-    private void announceItemRemoved(String suggestionTitle) {
+    SuggestionsSection getSectionForTesting(@CategoryInt int category) {
+        return mSections.get(category);
+    }
+
+    InnerNode getRootForTesting() {
+        return mRoot;
+    }
+
+    private void announceItemRemoved(String itemTitle) {
         // In tests the RecyclerView can be null.
         if (mRecyclerView == null) return;
 
         mRecyclerView.announceForAccessibility(mRecyclerView.getResources().getString(
-                R.string.ntp_accessibility_item_removed, suggestionTitle));
+                R.string.ntp_accessibility_item_removed, itemTitle));
     }
 
     private void announceItemRemoved(@StringRes int stringToAnnounce) {

chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/NewTabPageRecyclerView.java

@@ -185,7 +185,7 @@ public class NewTabPageRecyclerView extends RecyclerView implements TouchDisable
      * Updates the space added at the end of the list to make sure the above/below the fold
      * distinction can be preserved.
      */
-    public void refreshBottomSpacing() {
+    private void refreshBottomSpacing() {
         ViewHolder bottomSpacingViewHolder = findBottomSpacer();
 
         // It might not be in the layout yet if it's not visible or ready to be displayed.
@@ -536,8 +536,8 @@ public class NewTabPageRecyclerView extends RecyclerView implements TouchDisable
      * @param dX The amount of horizontal displacement caused by user's action.
      * @param viewHolder The view holder containing the view to be updated.
      */
-    public void updateViewStateForDismiss(float dX, ViewHolder viewHolder) {
-        if (!((NewTabPageViewHolder) viewHolder).isDismissable()) return;
+    public void updateViewStateForDismiss(float dX, NewTabPageViewHolder viewHolder) {
+        if (!viewHolder.isDismissable()) return;
 
         viewHolder.itemView.setTranslationX(dX);
 

chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/SuggestionsSection.java

@@ -50,7 +50,7 @@ public class SuggestionsSection extends InnerNode {
         mOfflinePageBridge = offlinePageBridge;
 
         mHeader = new SectionHeader(info.getTitle());
-        mSuggestionsList = new SuggestionsList(this);
+        mSuggestionsList = new SuggestionsList(this, info);
         mStatus = StatusItem.createNoSuggestionsItem(this);
         mMoreButton = new ActionItem(this);
         mProgressIndicator = new ProgressItem(this);
@@ -61,9 +61,11 @@ public class SuggestionsSection extends InnerNode {
 
     private static class SuggestionsList extends ChildNode implements Iterable<SnippetArticle> {
         private final List<SnippetArticle> mSuggestions = new ArrayList<>();
+        private final SuggestionsCategoryInfo mCategoryInfo;
 
-        public SuggestionsList(NodeParent parent) {
+        public SuggestionsList(NodeParent parent, SuggestionsCategoryInfo categoryInfo) {
             super(parent);
+            mCategoryInfo = categoryInfo;
         }
 
         @Override
@@ -80,7 +82,8 @@ public class SuggestionsSection extends InnerNode {
         @Override
         public void onBindViewHolder(NewTabPageViewHolder holder, int position) {
             assert holder instanceof SnippetArticleViewHolder;
-            ((SnippetArticleViewHolder) holder).onBindViewHolder(getSuggestionAt(position));
+            ((SnippetArticleViewHolder) holder)
+                    .onBindViewHolder(getSuggestionAt(position), mCategoryInfo);
         }
 
         @Override

chrome/android/java/src/org/chromium/chrome/browser/ntp/snippets/SnippetArticleViewHolder.java

@@ -66,6 +66,7 @@ public class SnippetArticleViewHolder
 
     private FetchImageCallback mImageCallback;
     private SnippetArticle mArticle;
+    private SuggestionsCategoryInfo mCategoryInfo;
     private int mPublisherFaviconSizePx;
 
     private final boolean mUseFaviconService;
@@ -149,10 +150,9 @@ public class SnippetArticleViewHolder
      * Updates the layout taking into account screen dimensions and the type of snippet displayed.
      */
     private void updateLayout() {
-        SuggestionsCategoryInfo info =
-                mRecyclerView.getNewTabPageAdapter().getCategoryInfo(mArticle.mCategory);
         boolean narrow = mUiConfig.getCurrentDisplayStyle() == UiConfig.DISPLAY_STYLE_NARROW;
-        boolean minimal = info.getCardLayout() == ContentSuggestionsCardLayout.MINIMAL_CARD;
+        boolean minimal =
+                mCategoryInfo.getCardLayout() == ContentSuggestionsCardLayout.MINIMAL_CARD;
 
         // If the screen is narrow or we are using the minimal layout, hide the article snippet.
         boolean hideSnippet = narrow || minimal;
@@ -185,13 +185,14 @@ public class SnippetArticleViewHolder
         mPublisherBar.setLayoutParams(params);
     }
 
-    public void onBindViewHolder(SnippetArticle article) {
+    public void onBindViewHolder(SnippetArticle article, SuggestionsCategoryInfo categoryInfo) {
         super.onBindViewHolder();
 
         // No longer listen for offline status changes to the old article.
         if (mArticle != null) mArticle.setOfflineStatusChangeRunnable(null);
 
         mArticle = article;
+        mCategoryInfo = categoryInfo;
         updateLayout();
 
         mHeadlineTextView.setText(mArticle.mTitle);

chrome/android/javatests/src/org/chromium/chrome/browser/ntp/cards/NewTabPageRecyclerViewTest.java

@@ -117,7 +117,7 @@ public class NewTabPageRecyclerViewTest extends ChromeTabbedActivityTestBase {
 
         // Scroll the last suggestion into view and click it.
         SnippetArticle suggestion = suggestions.get(suggestions.size() - 1);
-        int suggestionPosition = getAdapter().getSuggestionPosition(suggestion);
+        int suggestionPosition = getSuggestionPosition(suggestion);
         scrollToPosition(suggestionPosition);
         final View suggestionView = waitForView(suggestionPosition);
         ChromeTabUtils.waitForTabPageLoaded(mTab, new Runnable() {
@@ -135,12 +135,13 @@ public class NewTabPageRecyclerViewTest extends ChromeTabbedActivityTestBase {
     public void testAllDismissed() throws InterruptedException, TimeoutException {
         setSuggestionsAndWaitForUpdate(3);
         assertEquals(3, mSource.getSuggestionsForCategory(KnownCategories.ARTICLES).size());
-        assertFalse(getAdapter().hasAllBeenDismissed());
+        assertEquals(RecyclerView.NO_POSITION,
+                getAdapter().getFirstPositionForType(ItemViewType.ALL_DISMISSED));
         assertEquals(1, mSource.getCategories().length);
         assertEquals(KnownCategories.ARTICLES, mSource.getCategories()[0]);
 
         // Dismiss the sign in promo.
-        int signinPromoPosition = getAdapter().getSignInPromoPosition();
+        int signinPromoPosition = getAdapter().getFirstPositionForType(ItemViewType.PROMO);
         scrollToPosition(signinPromoPosition);
         View signinPromoView = waitForView(signinPromoPosition);
         getAdapter().dismissItem(signinPromoPosition);
@@ -155,11 +156,11 @@ public class NewTabPageRecyclerViewTest extends ChromeTabbedActivityTestBase {
             waitForViewToDetach(cardView);
             cardPosition = getAdapter().getFirstCardPosition();
         }
-        assertTrue(getAdapter().hasAllBeenDismissed());
         assertEquals(0, mSource.getCategories().length);
 
         // Click the refresh button on the all dismissed item.
-        int allDismissedPosition = getAdapter().getLastContentItemPosition();
+        int allDismissedPosition = getAdapter().getFirstPositionForType(ItemViewType.ALL_DISMISSED);
+        assertTrue(allDismissedPosition != RecyclerView.NO_POSITION);
         scrollToPosition(allDismissedPosition);
         View allDismissedView = waitForView(allDismissedPosition);
         singleClickView(allDismissedView.findViewById(R.id.action_button));
@@ -178,8 +179,7 @@ public class NewTabPageRecyclerViewTest extends ChromeTabbedActivityTestBase {
         assertEquals(10, suggestions.size());
 
         // Scroll a suggestion into view.
-        int suggestionPosition =
-                getAdapter().getSuggestionPosition(suggestions.get(suggestions.size() - 1));
+        int suggestionPosition = getSuggestionPosition(suggestions.get(suggestions.size() - 1));
         scrollToPosition(suggestionPosition);
         View suggestionView = waitForView(suggestionPosition);
 
@@ -246,6 +246,15 @@ public class NewTabPageRecyclerViewTest extends ChromeTabbedActivityTestBase {
         return getRecyclerView().getNewTabPageAdapter();
     }
 
+    private int getSuggestionPosition(SnippetArticle article) {
+        NewTabPageAdapter adapter = getAdapter();
+        for (int i = 0; i < adapter.getItemCount(); i++) {
+            SnippetArticle articleToCheck = adapter.getSuggestionAt(i);
+            if (articleToCheck != null && articleToCheck.equals(article)) return i;
+        }
+        return RecyclerView.NO_POSITION;
+    }
+
     private void scrollToPosition(final int position) {
         final NewTabPageRecyclerView recyclerView = getRecyclerView();
 

chrome/android/junit/src/org/chromium/chrome/browser/ntp/cards/NewTabPageAdapterTest.java

@@ -6,10 +6,10 @@ package org.chromium.chrome.browser.ntp.cards;
 
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotEquals;
 import static org.junit.Assert.assertThat;
 import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.fail;
-import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.Mockito.atLeastOnce;
 import static org.mockito.Mockito.doNothing;
 import static org.mockito.Mockito.mock;
@@ -74,10 +74,12 @@ public class NewTabPageAdapterTest {
 
     private FakeSuggestionsSource mSource;
     private NewTabPageAdapter mAdapter;
+    @Mock
     private SigninManager mMockSigninManager;
     @Mock
     private OfflinePageBridge mOfflinePageBridge;
-    @Mock private NewTabPageManager mNewTabPageManager;
+    @Mock
+    private NewTabPageManager mNewTabPageManager;
 
     /**
      * Stores information about a section that should be present in the adapter.
@@ -109,19 +111,19 @@ public class NewTabPageAdapterTest {
      * expressed as a sequence of calls to the {@link #expect} methods.
      */
     private static class ItemsMatcher { // TODO(pke): Find better name.
-        private final NewTabPageAdapter mAdapter;
+        private final TreeNode mTreeNode;
         private int mCurrentIndex;
 
-        public ItemsMatcher(NewTabPageAdapter adapter, int startingIndex) {
-            mAdapter = adapter;
-            mCurrentIndex = startingIndex;
+        public ItemsMatcher(TreeNode root) {
+            mTreeNode = root;
         }
 
         public void expect(@ItemViewType int expectedItemType) {
-            if (mCurrentIndex >= mAdapter.getItemCount()) {
+            if (mCurrentIndex >= mTreeNode.getItemCount()) {
                 fail("Expected item of type " + expectedItemType + " but encountered end of list");
             }
-            @ItemViewType int itemType = mAdapter.getItemViewType(mCurrentIndex);
+            @ItemViewType
+            int itemType = mTreeNode.getItemViewType(mCurrentIndex);
             assertEquals("Type mismatch at position " + mCurrentIndex, expectedItemType, itemType);
             mCurrentIndex++;
         }
@@ -146,63 +148,9 @@ public class NewTabPageAdapterTest {
             }
         }
 
-        public void expectPosition(int expectedPosition) {
-            assertEquals(expectedPosition, mCurrentIndex);
-        }
-    }
-
-    /**
-     * Asserts that the given {@link TreeNode} is a {@link SuggestionsSection} that matches the
-     * given {@link SectionDescriptor}.
-     * @param descriptor The section descriptor to match against.
-     * @param node The node from the adapter.
-     */
-    private void assertMatches(SectionDescriptor descriptor, TreeNode node) {
-        int offset = mAdapter.getChildPositionOffset(node);
-        ItemsMatcher matcher = new ItemsMatcher(mAdapter, offset);
-        matcher.expect(descriptor);
-        matcher.expectPosition(offset + node.getItemCount());
-    }
-
-    /**
-     * Asserts that {@link #mAdapter}.{@link NewTabPageAdapter#getItemCount()} corresponds to an
-     * NTP with the given sections in it.
-     * @param descriptors A list of descriptors, each describing a section that should be present on
-     *                    the UI.
-     */
-    private void assertItemsFor(SectionDescriptor... descriptors) {
-        ItemsMatcher matcher = new ItemsMatcher(mAdapter, 0);
-        matcher.expect(ItemViewType.ABOVE_THE_FOLD);
-        for (SectionDescriptor descriptor : descriptors) matcher.expect(descriptor);
-        if (descriptors.length == 0) {
-            matcher.expect(ItemViewType.ALL_DISMISSED);
-        } else {
-            matcher.expect(ItemViewType.FOOTER);
+        public void expectEnd() {
+            assertEquals(mTreeNode.getItemCount(), mCurrentIndex);
         }
-        matcher.expect(ItemViewType.SPACING);
-        matcher.expectPosition(mAdapter.getItemCount());
-    }
-
-    /**
-     * To be used with {@link #assertItemsFor(SectionDescriptor...)}, for a section with
-     * {@code numSuggestions} cards in it.
-     * @param numSuggestions The number of suggestions in the section. If there are zero, use either
-     *                       no section at all (if it is not displayed) or
-     *                       {@link #sectionWithStatusCard()}.
-     * @return A descriptor for the section.
-     */
-    private SectionDescriptor section(int numSuggestions) {
-        assert numSuggestions > 0;
-        return new SectionDescriptor(numSuggestions);
-    }
-
-    /**
-     * To be used with {@link #assertItemsFor(SectionDescriptor...)}, for a section that has no
-     * suggestions, but a status card to be displayed.
-     * @return A descriptor for the section.
-     */
-    private SectionDescriptor sectionWithStatusCard() {
-        return new SectionDescriptor(0);
     }
 
     @Before
@@ -212,7 +160,6 @@ public class NewTabPageAdapterTest {
         // Initialise the sign in state. We will be signed in by default in the tests.
         assertFalse(ChromePreferenceManager.getInstance(RuntimeEnvironment.application)
                             .getNewTabPageSigninPromoDismissed());
-        mMockSigninManager = mock(SigninManager.class);
         SigninManager.setInstanceForTesting(mMockSigninManager);
         when(mMockSigninManager.isSignedInOnNative()).thenReturn(true);
         when(mMockSigninManager.isSignInAllowed()).thenReturn(true);
@@ -230,7 +177,7 @@ public class NewTabPageAdapterTest {
         when(mNewTabPageManager.getSuggestionsSource()).thenReturn(mSource);
         when(mNewTabPageManager.isCurrentPage()).thenReturn(true);
 
-        mAdapter = new NewTabPageAdapter(mNewTabPageManager, null, null, mOfflinePageBridge);
+        reloadNtp();
     }
 
     @After
@@ -361,8 +308,7 @@ public class NewTabPageAdapterTest {
     @Test
     @Feature({"Ntp"})
     public void testProgressIndicatorDisplay() {
-        int progressPos = mAdapter.getFirstPositionForType(ItemViewType.FOOTER) - 1;
-        SuggestionsSection section = mAdapter.getSuggestionsSection(progressPos);
+        SuggestionsSection section = mAdapter.getSectionForTesting(KnownCategories.ARTICLES);
         ProgressItem progress = section.getProgressItemForTesting();
 
         mSource.setStatusForCategory(KnownCategories.ARTICLES, CategoryStatus.INITIALIZING);
@@ -395,20 +341,19 @@ public class NewTabPageAdapterTest {
         assertItemsFor();
 
         // Same when loading a new NTP.
-        mAdapter = new NewTabPageAdapter(mNewTabPageManager, null, null, mOfflinePageBridge);
+        reloadNtp();
         assertItemsFor();
 
         // Same for CATEGORY_EXPLICITLY_DISABLED.
         mSource.setStatusForCategory(KnownCategories.ARTICLES, CategoryStatus.AVAILABLE);
         mSource.setSuggestionsForCategory(KnownCategories.ARTICLES, snippets);
-        mAdapter = new NewTabPageAdapter(mNewTabPageManager, null, null, mOfflinePageBridge);
+        reloadNtp();
         assertItemsFor(section(5));
         mSource.setStatusForCategory(
                 KnownCategories.ARTICLES, CategoryStatus.CATEGORY_EXPLICITLY_DISABLED);
         assertItemsFor();
 
-        // Same when loading a new NTP.
-        mAdapter = new NewTabPageAdapter(mNewTabPageManager, null, null, mOfflinePageBridge);
+        reloadNtp();
         assertItemsFor();
     }
 
@@ -428,8 +373,7 @@ public class NewTabPageAdapterTest {
         mSource.silentlyRemoveCategory(KnownCategories.ARTICLES);
         assertItemsFor(section(4));
 
-        // But it disappears when loading a new NTP.
-        mAdapter = new NewTabPageAdapter(mNewTabPageManager, null, null, mOfflinePageBridge);
+        reloadNtp();
         assertItemsFor();
     }
 
@@ -439,31 +383,27 @@ public class NewTabPageAdapterTest {
     public void testSectionVisibleIfEmpty() {
         @CategoryInt
         final int category = 42;
-        final int sectionIdx = 1; // section 0 is the above-the-fold item, we test the one after.
-        final List<SnippetArticle> articles =
-                Collections.unmodifiableList(createDummySuggestions(3));
-        FakeSuggestionsSource suggestionsSource;
 
         // Part 1: VisibleIfEmpty = true
-        suggestionsSource = new FakeSuggestionsSource();
+        FakeSuggestionsSource suggestionsSource = new FakeSuggestionsSource();
         suggestionsSource.setStatusForCategory(category, CategoryStatus.INITIALIZING);
         suggestionsSource.setInfoForCategory(category,
                 new CategoryInfoBuilder(category).showIfEmpty().build());
 
         // 1.1 - Initial state
         when(mNewTabPageManager.getSuggestionsSource()).thenReturn(suggestionsSource);
-        mAdapter = new NewTabPageAdapter(mNewTabPageManager, null, null, mOfflinePageBridge);
+        reloadNtp();
         assertItemsFor(sectionWithStatusCard().withProgress());
 
         // 1.2 - With suggestions
+        List<SnippetArticle> articles = Collections.unmodifiableList(createDummySuggestions(3));
         suggestionsSource.setStatusForCategory(category, CategoryStatus.AVAILABLE);
         suggestionsSource.setSuggestionsForCategory(category, articles);
         assertItemsFor(section(3));
 
         // 1.3 - When all suggestions are dismissed
-        assertEquals(SuggestionsSection.class, mAdapter.getChildren().get(sectionIdx).getClass());
-        SuggestionsSection section42 = (SuggestionsSection) mAdapter.getChildren().get(sectionIdx);
-        assertMatches(section(3), section42);
+        SuggestionsSection section42 = mAdapter.getSectionForTesting(category);
+        assertSectionMatches(section(3), section42);
         section42.removeSuggestion(articles.get(0));
         section42.removeSuggestion(articles.get(1));
         section42.removeSuggestion(articles.get(2));
@@ -476,7 +416,7 @@ public class NewTabPageAdapterTest {
 
         // 2.1 - Initial state
         when(mNewTabPageManager.getSuggestionsSource()).thenReturn(suggestionsSource);
-        mAdapter = new NewTabPageAdapter(mNewTabPageManager, null, null, mOfflinePageBridge);
+        reloadNtp();
         assertItemsFor();
 
         // 2.2 - With suggestions
@@ -495,14 +435,9 @@ public class NewTabPageAdapterTest {
     public void testMoreButton() {
         @CategoryInt
         final int category = 42;
-        final int sectionIdx = 1; // section 0 is the above the fold, we test the one after.
-        final List<SnippetArticle> articles =
-                Collections.unmodifiableList(createDummySuggestions(3));
-        FakeSuggestionsSource suggestionsSource;
-        SuggestionsSection section42;
 
         // Part 1: With "View All" action
-        suggestionsSource = new FakeSuggestionsSource();
+        FakeSuggestionsSource suggestionsSource = new FakeSuggestionsSource();
         suggestionsSource.setStatusForCategory(category, CategoryStatus.INITIALIZING);
         suggestionsSource.setInfoForCategory(category, new CategoryInfoBuilder(category)
                                                                .withViewAllAction()
@@ -511,18 +446,18 @@ public class NewTabPageAdapterTest {
 
         // 1.1 - Initial state.
         when(mNewTabPageManager.getSuggestionsSource()).thenReturn(suggestionsSource);
-        mAdapter = new NewTabPageAdapter(mNewTabPageManager, null, null, mOfflinePageBridge);
+        reloadNtp();
         assertItemsFor(sectionWithStatusCard().withActionButton().withProgress());
 
         // 1.2 - With suggestions.
+        List<SnippetArticle> articles = Collections.unmodifiableList(createDummySuggestions(3));
         suggestionsSource.setStatusForCategory(category, CategoryStatus.AVAILABLE);
         suggestionsSource.setSuggestionsForCategory(category, articles);
         assertItemsFor(section(3).withActionButton());
 
         // 1.3 - When all suggestions are dismissed.
-        assertEquals(SuggestionsSection.class, mAdapter.getChildren().get(sectionIdx).getClass());
-        section42 = (SuggestionsSection) mAdapter.getChildren().get(sectionIdx);
-        assertMatches(section(3).withActionButton(), section42);
+        SuggestionsSection section42 = mAdapter.getSectionForTesting(category);
+        assertSectionMatches(section(3).withActionButton(), section42);
         section42.removeSuggestion(articles.get(0));
         section42.removeSuggestion(articles.get(1));
         section42.removeSuggestion(articles.get(2));
@@ -536,7 +471,7 @@ public class NewTabPageAdapterTest {
 
         // 2.1 - Initial state.
         when(mNewTabPageManager.getSuggestionsSource()).thenReturn(suggestionsSource);
-        mAdapter = new NewTabPageAdapter(mNewTabPageManager, null, null, mOfflinePageBridge);
+        reloadNtp();
         assertItemsFor(sectionWithStatusCard().withProgress());
 
         // 2.2 - With suggestions.
@@ -545,22 +480,14 @@ public class NewTabPageAdapterTest {
         assertItemsFor(section(3));
 
         // 2.3 - When all suggestions are dismissed.
-        assertEquals(SuggestionsSection.class, mAdapter.getChildren().get(sectionIdx).getClass());
-        section42 = (SuggestionsSection) mAdapter.getChildren().get(sectionIdx);
-        assertMatches(section(3), section42);
+        section42 = mAdapter.getSectionForTesting(category);
+        assertSectionMatches(section(3), section42);
         section42.removeSuggestion(articles.get(0));
         section42.removeSuggestion(articles.get(1));
         section42.removeSuggestion(articles.get(2));
         assertItemsFor(sectionWithStatusCard());
     }
 
-    private void assertArticlesEqual(List<SnippetArticle> articles, int start, int end) {
-        assertThat(mAdapter.getItemCount(), greaterThanOrEqualTo(end));
-        for (int i = start; i < end; i++) {
-            assertEquals(articles.get(i - start), mAdapter.getSuggestionAt(i));
-        }
-    }
-
     /**
      * Tests that invalidated suggestions are immediately removed.
      */
@@ -596,8 +523,7 @@ public class NewTabPageAdapterTest {
                                                              .build());
         mSource.setStatusForCategory(dynamicCategory1, CategoryStatus.AVAILABLE);
         mSource.setSuggestionsForCategory(dynamicCategory1, dynamics1);
-        // Reload
-        mAdapter = new NewTabPageAdapter(mNewTabPageManager, null, null, mOfflinePageBridge);
+        reloadNtp();
 
         assertItemsFor(section(3), section(5).withActionButton());
 
@@ -607,8 +533,7 @@ public class NewTabPageAdapterTest {
                 new CategoryInfoBuilder(dynamicCategory1).build());
         mSource.setStatusForCategory(dynamicCategory2, CategoryStatus.AVAILABLE);
         mSource.setSuggestionsForCategory(dynamicCategory2, dynamics2);
-        // Reload
-        mAdapter = new NewTabPageAdapter(mNewTabPageManager, null, null, mOfflinePageBridge);
+        reloadNtp();
         assertItemsFor(section(3), section(5).withActionButton(), section(11));
     }
 
@@ -621,16 +546,14 @@ public class NewTabPageAdapterTest {
         // Above-the-fold, sign in promo, all-dismissed, footer, spacer.
         final int basicChildCount = 5;
         FakeSuggestionsSource suggestionsSource = new FakeSuggestionsSource();
+        when(mNewTabPageManager.getSuggestionsSource()).thenReturn(suggestionsSource);
         registerCategory(suggestionsSource, KnownCategories.ARTICLES, 0);
         registerCategory(suggestionsSource, KnownCategories.BOOKMARKS, 0);
         registerCategory(suggestionsSource, KnownCategories.PHYSICAL_WEB_PAGES, 0);
         registerCategory(suggestionsSource, KnownCategories.DOWNLOADS, 0);
+        reloadNtp();
 
-        when(mNewTabPageManager.getSuggestionsSource()).thenReturn(suggestionsSource);
-        NewTabPageAdapter ntpAdapter = new NewTabPageAdapter(
-                mNewTabPageManager, null, null, mOfflinePageBridge);
-        List<TreeNode> children = ntpAdapter.getChildren();
-
+        List<TreeNode> children = mAdapter.getRootForTesting().getChildren();
         assertEquals(basicChildCount + 4, children.size());
         assertEquals(AboveTheFoldItem.class, children.get(0).getClass());
         assertEquals(SuggestionsSection.class, children.get(1).getClass());
@@ -644,16 +567,14 @@ public class NewTabPageAdapterTest {
 
         // With a different order.
         suggestionsSource = new FakeSuggestionsSource();
+        when(mNewTabPageManager.getSuggestionsSource()).thenReturn(suggestionsSource);
         registerCategory(suggestionsSource, KnownCategories.ARTICLES, 0);
         registerCategory(suggestionsSource, KnownCategories.PHYSICAL_WEB_PAGES, 0);
         registerCategory(suggestionsSource, KnownCategories.DOWNLOADS, 0);
         registerCategory(suggestionsSource, KnownCategories.BOOKMARKS, 0);
+        reloadNtp();
 
-        when(mNewTabPageManager.getSuggestionsSource()).thenReturn(suggestionsSource);
-        ntpAdapter = new NewTabPageAdapter(
-                mNewTabPageManager, null, null, mOfflinePageBridge);
-        children = ntpAdapter.getChildren();
-
+        children = mAdapter.getRootForTesting().getChildren();
         assertEquals(basicChildCount + 4, children.size());
         assertEquals(AboveTheFoldItem.class, children.get(0).getClass());
         assertEquals(SuggestionsSection.class, children.get(1).getClass());
@@ -667,19 +588,17 @@ public class NewTabPageAdapterTest {
 
         // With unknown categories.
         suggestionsSource = new FakeSuggestionsSource();
+        when(mNewTabPageManager.getSuggestionsSource()).thenReturn(suggestionsSource);
         registerCategory(suggestionsSource, KnownCategories.ARTICLES, 0);
         registerCategory(suggestionsSource, KnownCategories.PHYSICAL_WEB_PAGES, 0);
         registerCategory(suggestionsSource, KnownCategories.DOWNLOADS, 0);
-
-        when(mNewTabPageManager.getSuggestionsSource()).thenReturn(suggestionsSource);
-        ntpAdapter = new NewTabPageAdapter(mNewTabPageManager, null, null, mOfflinePageBridge);
+        reloadNtp();
 
         // The adapter is already initialised, it will not accept new categories anymore.
         registerCategory(suggestionsSource, 42, 1);
         registerCategory(suggestionsSource, KnownCategories.BOOKMARKS, 1);
 
-        children = ntpAdapter.getChildren();
-
+        children = mAdapter.getRootForTesting().getChildren();
         assertEquals(basicChildCount + 3, children.size());
         assertEquals(AboveTheFoldItem.class, children.get(0).getClass());
         assertEquals(SuggestionsSection.class, children.get(1).getClass());
@@ -694,16 +613,12 @@ public class NewTabPageAdapterTest {
     @Feature({"Ntp"})
     public void testChangeNotifications() {
         FakeSuggestionsSource suggestionsSource = spy(new FakeSuggestionsSource());
-        // Allow using dismissSuggestion() instead of throwing UnsupportedOperationException.
-        doNothing().when(suggestionsSource).dismissSuggestion(any(SnippetArticle.class));
-
         registerCategory(suggestionsSource, KnownCategories.ARTICLES, 3);
         when(mNewTabPageManager.getSuggestionsSource()).thenReturn(suggestionsSource);
-        NewTabPageAdapter adapter = new NewTabPageAdapter(
-                mNewTabPageManager, null, null, mOfflinePageBridge);
+
+        reloadNtp();
         AdapterDataObserver dataObserver = mock(AdapterDataObserver.class);
-        adapter.registerAdapterDataObserver(dataObserver);
-        reset(dataObserver); // reset notification changes from initialisation.
+        mAdapter.registerAdapterDataObserver(dataObserver);
 
         // Adapter content:
         // Idx | Item
@@ -714,24 +629,26 @@ public class NewTabPageAdapterTest {
         // 5   | Footer
         // 6   | Spacer
 
-        adapter.dismissItem(3); // Dismiss the second suggestion of the second section.
+        mAdapter.dismissItem(3); // Dismiss the second suggestion of the second section.
         verify(dataObserver).onItemRangeRemoved(3, 1);
         verify(dataObserver).onItemRangeChanged(5, 1, null);
 
         // Make sure the call with the updated position works properly.
-        adapter.dismissItem(3);
+        mAdapter.dismissItem(3);
         verify(dataObserver, times(2)).onItemRangeRemoved(3, 1);
         verify(dataObserver).onItemRangeChanged(4, 1, null);
-        reset(dataObserver);
+        verifyNoMoreInteractions(dataObserver);
 
         // Dismiss the last suggestion in the section. We should now show the status card.
-        adapter.dismissItem(2);
+        reset(dataObserver);
+        mAdapter.dismissItem(2);
         verify(dataObserver).onItemRangeRemoved(2, 1); // Suggestion removed
         verify(dataObserver).onItemRangeChanged(3, 1, null); // Spacer refresh
         verify(dataObserver).onItemRangeInserted(2, 1); // Status card added
         verify(dataObserver).onItemRangeChanged(4, 1, null); // Spacer refresh
         verify(dataObserver).onItemRangeInserted(3, 1); // Action item added
         verify(dataObserver).onItemRangeChanged(5, 1, null); // Spacer refresh
+        verifyNoMoreInteractions(dataObserver);
 
         // Adapter content:
         // Idx | Item
@@ -748,7 +665,7 @@ public class NewTabPageAdapterTest {
         reset(dataObserver);
         suggestionsSource.setSuggestionsForCategory(
                 KnownCategories.ARTICLES, createDummySuggestions(newSuggestionCount));
-        adapter.onNewSuggestions(KnownCategories.ARTICLES);
+        mAdapter.onNewSuggestions(KnownCategories.ARTICLES);
         verify(dataObserver).onItemRangeInserted(2, newSuggestionCount);
         verify(dataObserver).onItemRangeChanged(5 + newSuggestionCount, 1, null); // Spacer refresh
         verify(dataObserver, times(2)).onItemRangeRemoved(2 + newSuggestionCount, 1);
@@ -768,13 +685,14 @@ public class NewTabPageAdapterTest {
         reset(dataObserver);
         suggestionsSource.setSuggestionsForCategory(
                 KnownCategories.ARTICLES, createDummySuggestions(0));
-        adapter.onCategoryStatusChanged(KnownCategories.ARTICLES, CategoryStatus.SIGNED_OUT);
+        mAdapter.onCategoryStatusChanged(KnownCategories.ARTICLES, CategoryStatus.SIGNED_OUT);
         verify(dataObserver).onItemRangeRemoved(2, newSuggestionCount);
         verify(dataObserver).onItemRangeChanged(3, 1, null); // Spacer refresh
         verify(dataObserver).onItemRangeInserted(2, 1); // Status card added
         verify(dataObserver).onItemRangeChanged(4, 1, null); // Spacer refresh
         verify(dataObserver).onItemRangeInserted(3, 1); // Action item added
         verify(dataObserver).onItemRangeChanged(5, 1, null); // Spacer refresh
+        verifyNoMoreInteractions(dataObserver);
     }
 
     @Test
@@ -787,27 +705,8 @@ public class NewTabPageAdapterTest {
 
         doNothing().when(mNewTabPageManager).addDestructionObserver(observers.capture());
 
-        NewTabPageAdapter adapter =
-                new NewTabPageAdapter(mNewTabPageManager, null, null, mOfflinePageBridge);
-
-        TreeNode signinPromo = adapter.getChildren().get(2);
-
-        // Adapter content:
-        // Idx | Item               | Item Index
-        // ----|--------------------|-------------
-        // 0   | Above-the-fold     | 0
-        // 1   | Header             | 1
-        // 2   | Status             | 1
-        // 3   | Action             | 1
-        // 4   | Progress Indicator | 1
-        // 5   | Sign in promo      | 2
-        // 6   | Footer             | 3
-        // 7   | Spacer             | 4
-
-        assertEquals(1, signinPromo.getItemCount());
-        assertEquals(ItemViewType.PROMO, signinPromo.getItemViewType(0));
-
-        // verify(mNewTabPageManager).addDestructionObserver(observers.capture());
+        reloadNtp();
+        assertTrue(isSignInPromoVisible());
 
         // Note: As currently implemented, these two variables should point to the same object, a
         // SignInPromo.SigninObserver
@@ -823,18 +722,18 @@ public class NewTabPageAdapterTest {
         }
 
         signInStateObserver.onSignedIn();
-        assertEquals(0, signinPromo.getItemCount());
+        assertFalse(isSignInPromoVisible());
 
         signInStateObserver.onSignedOut();
-        assertEquals(1, signinPromo.getItemCount());
+        assertTrue(isSignInPromoVisible());
 
         when(mMockSigninManager.isSignInAllowed()).thenReturn(false);
         signInAllowedObserver.onSignInAllowedChanged();
-        assertEquals(0, signinPromo.getItemCount());
+        assertFalse(isSignInPromoVisible());
 
         when(mMockSigninManager.isSignInAllowed()).thenReturn(true);
         signInAllowedObserver.onSignInAllowedChanged();
-        assertEquals(1, signinPromo.getItemCount());
+        assertTrue(isSignInPromoVisible());
     }
 
     @Test
@@ -844,38 +743,18 @@ public class NewTabPageAdapterTest {
         when(mMockSigninManager.isSignedInOnNative()).thenReturn(false);
         ChromePreferenceManager.getInstance(RuntimeEnvironment.application)
                 .setNewTabPageSigninPromoDismissed(false);
+        reloadNtp();
 
-        NewTabPageAdapter adapter =
-                new NewTabPageAdapter(mNewTabPageManager, null, null, mOfflinePageBridge);
-        final int signInPromoIndex = adapter.getFirstPositionForType(ItemViewType.PROMO);
-
-        assertEquals(6, adapter.getChildren().size());
-        TreeNode signinPromo = adapter.getChildren().get(2);
+        final int signInPromoPosition = mAdapter.getFirstPositionForType(ItemViewType.PROMO);
+        assertNotEquals(RecyclerView.NO_POSITION, signInPromoPosition);
+        mAdapter.dismissItem(signInPromoPosition);
 
-        // Adapter content:
-        // Idx | Item               | Item Index
-        // ----|--------------------|-------------
-        // 0   | Above-the-fold     | 0
-        // 1   | Header             | 1
-        // 2   | Status             | 1
-        // 3   | Action             | 1
-        // 4   | Progress Indicator | 1
-        // 5   | Sign in promo      | 2
-        // 6   | All dismissed      | 3
-        // 7   | Footer             | 4
-        // 8   | Spacer             | 5
-
-        assertEquals(ItemViewType.PROMO, signinPromo.getItemViewType(0));
-
-        adapter.dismissItem(signInPromoIndex);
-        assertEquals(0, signinPromo.getItemCount());
+        assertFalse(isSignInPromoVisible());
         assertTrue(ChromePreferenceManager.getInstance(RuntimeEnvironment.application)
                            .getNewTabPageSigninPromoDismissed());
 
-        adapter = new NewTabPageAdapter(mNewTabPageManager, null, null, mOfflinePageBridge);
-        assertEquals(6, adapter.getChildren().size());
-        // The items below the signin promo move up, footer is now at the position of the promo.
-        assertEquals(ItemViewType.FOOTER, adapter.getItemViewType(signInPromoIndex));
+        reloadNtp();
+        assertFalse(isSignInPromoVisible());
     }
 
     @Test
@@ -987,6 +866,75 @@ public class NewTabPageAdapterTest {
                 mAdapter.getFirstPositionForType(ItemViewType.ALL_DISMISSED));
     }
 
+    /**
+     * Asserts that the given {@link TreeNode} is a {@link SuggestionsSection} that matches the
+     * given {@link SectionDescriptor}.
+     * @param descriptor The section descriptor to match against.
+     * @param section The section from the adapter.
+     */
+    private void assertSectionMatches(SectionDescriptor descriptor, SuggestionsSection section) {
+        ItemsMatcher matcher = new ItemsMatcher(section);
+        matcher.expect(descriptor);
+        matcher.expectEnd();
+    }
+
+    /**
+     * Asserts that {@link #mAdapter}.{@link NewTabPageAdapter#getItemCount()} corresponds to an NTP
+     * with the given sections in it.
+     *
+     * @param descriptors A list of descriptors, each describing a section that should be present on
+     *                    the UI.
+     */
+    private void assertItemsFor(SectionDescriptor... descriptors) {
+        ItemsMatcher matcher = new ItemsMatcher(mAdapter.getRootForTesting());
+        matcher.expect(ItemViewType.ABOVE_THE_FOLD);
+        for (SectionDescriptor descriptor : descriptors) matcher.expect(descriptor);
+        if (descriptors.length == 0) {
+            matcher.expect(ItemViewType.ALL_DISMISSED);
+        } else {
+            matcher.expect(ItemViewType.FOOTER);
+        }
+        matcher.expect(ItemViewType.SPACING);
+        matcher.expectEnd();
+    }
+
+    /**
+     * To be used with {@link #assertItemsFor(SectionDescriptor...)}, for a section with
+     * {@code numSuggestions} cards in it.
+     * @param numSuggestions The number of suggestions in the section. If there are zero, use either
+     *                       no section at all (if it is not displayed) or
+     *                       {@link #sectionWithStatusCard()}.
+     * @return A descriptor for the section.
+     */
+    private SectionDescriptor section(int numSuggestions) {
+        assert numSuggestions > 0;
+        return new SectionDescriptor(numSuggestions);
+    }
+
+    /**
+     * To be used with {@link #assertItemsFor(SectionDescriptor...)}, for a section that has no
+     * suggestions, but a status card to be displayed.
+     * @return A descriptor for the section.
+     */
+    private SectionDescriptor sectionWithStatusCard() {
+        return new SectionDescriptor(0);
+    }
+
+    private void reloadNtp() {
+        mAdapter = new NewTabPageAdapter(mNewTabPageManager, null, null, mOfflinePageBridge);
+    }
+
+    private void assertArticlesEqual(List<SnippetArticle> articles, int start, int end) {
+        assertThat(mAdapter.getItemCount(), greaterThanOrEqualTo(end));
+        for (int i = start; i < end; i++) {
+            assertEquals(articles.get(i - start), mAdapter.getSuggestionAt(i));
+        }
+    }
+
+    private boolean isSignInPromoVisible() {
+        return mAdapter.getFirstPositionForType(ItemViewType.PROMO) != RecyclerView.NO_POSITION;
+    }
+
     /** Registers the category with the reload action */
     private void registerCategory(FakeSuggestionsSource suggestionsSource,
             @CategoryInt int category, int suggestionCount) {