Fix file deletion after the move to Model IDs.

- Add methods to the DocumentsAdatper to hide and unhide files.  This
  removes that burden from the Model.

- Remove clunky markForDeletion/finalizeDeletion and all related code
  from the Model.  Replace with a straight-up delete method.

- Modify deletion code in the DirectoryFragment.  Deletion now looks
  like:
  - user presses delete
  - DocumentsAdapter hides the deleted files
  - If the user presses cancel, the DocumentsAdapter unhides the files.
  - If the user doesn't cancel, Model.delete is called to delete the
    files.

- Fix deletion-related Model tests.

BUG=26024369

Change-Id: I02e2131c1aff1ebcd0bdb93d374675fd157d7f51

5 files changed, 301 insertions, 300 deletions

diff --git a/packages/DocumentsUI/src/com/android/documentsui/dirlist/DirectoryFragment.java b/packages/DocumentsUI/src/com/android/documentsui/dirlist/DirectoryFragment.java
index 107ade891f73..b66a12441bf2 100644
--- a/packages/DocumentsUI/src/com/android/documentsui/dirlist/DirectoryFragment.java
+++ b/packages/DocumentsUI/src/com/android/documentsui/dirlist/DirectoryFragment.java
@@ -116,10 +116,12 @@ import com.android.documentsui.model.DocumentInfo;
 import com.android.documentsui.model.DocumentStack;
 import com.android.documentsui.model.RootInfo;
 import com.google.common.collect.Lists;
+import com.google.common.collect.Sets;
 
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
+import java.util.Set;
 
 /**
  * Display the documents inside a single directory.
@@ -844,8 +846,11 @@ public class DirectoryFragment extends Fragment {
         Context context = getActivity();
         String message = Shared.getQuantityString(context, R.plurals.deleting, selected.size());
 
-        mModel.markForDeletion(selected);
+        // Hide the files in the UI.
+        final SparseArray<String> toDelete = mAdapter.hide(selected.getAll());
 
+        // Show a snackbar informing the user that files will be deleted, and give them an option to
+        // cancel.
         final Activity activity = getActivity();
         Snackbars.makeSnackbar(activity, message, Snackbar.LENGTH_LONG)
                 .setAction(
@@ -859,19 +864,22 @@ public class DirectoryFragment extends Fragment {
                             @Override
                             public void onDismissed(Snackbar snackbar, int event) {
                                 if (event == Snackbar.Callback.DISMISS_EVENT_ACTION) {
-                                    mModel.undoDeletion();
+                                    // If the delete was cancelled, just unhide the files.
+                                    mAdapter.unhide(toDelete);
                                 } else {
-                                    mModel.finalizeDeletion(
+                                    // Actually kick off the delete.
+                                    mModel.delete(
+                                            selected,
                                             new Model.DeletionListener() {
                                                 @Override
-                                                public void onError() {
-                                                    Snackbars.makeSnackbar(
-                                                            activity,
-                                                            R.string.toast_failed_delete,
-                                                            Snackbar.LENGTH_LONG)
-                                                            .show();
-
-                                                }
+                                                  public void onError() {
+                                                      Snackbars.makeSnackbar(
+                                                              activity,
+                                                              R.string.toast_failed_delete,
+                                                              Snackbar.LENGTH_LONG)
+                                                              .show();
+
+                                                  }
                                             });
                                 }
                             }
@@ -1049,7 +1057,6 @@ public class DirectoryFragment extends Fragment {
 
         @Override
         public void onBindViewHolder(DocumentHolder holder, int position) {
-
             final Context context = getContext();
             final State state = getDisplayState();
             final RootsCache roots = DocumentsApplication.getRootsCache(context);
@@ -1239,6 +1246,45 @@ public class DirectoryFragment extends Fragment {
             return mModelIds.get(adapterPosition);
         }
 
+        /**
+         * Hides a set of items from the associated RecyclerView.
+         *
+         * @param ids The Model IDs of the items to hide.
+         * @return A SparseArray that maps the hidden IDs to their old positions. This can be used
+         *         to {@link #unhide} the items if necessary.
+         */
+        public SparseArray<String> hide(String... ids) {
+            Set<String> toHide = Sets.newHashSet(ids);
+
+            // Proceed backwards through the list of items, because each removal causes the
+            // positions of all subsequent items to change.
+            SparseArray<String> hiddenItems = new SparseArray<>();
+            for (int i = mModelIds.size() - 1; i >= 0; --i) {
+                String id = mModelIds.get(i);
+                if (toHide.contains(id)) {
+                    hiddenItems.put(i, mModelIds.remove(i));
+                    notifyItemRemoved(i);
+                }
+            }
+
+            return hiddenItems;
+        }
+
+        /**
+         * Unhides a set of previously hidden items.
+         *
+         * @param ids A sparse array of IDs from a previous call to {@link #hide}.
+         */
+        public void unhide(SparseArray<String> ids) {
+            // Proceed backwards through the list of items, because each addition causes the
+            // positions of all subsequent items to change.
+            for (int i = ids.size() - 1; i >= 0; --i) {
+                int pos = ids.keyAt(i);
+                String id = ids.get(pos);
+                mModelIds.add(pos, id);
+                notifyItemInserted(pos);
+            }
+        }
     }
 
     private static String formatTime(Context context, long when) {
diff --git a/packages/DocumentsUI/src/com/android/documentsui/dirlist/Model.java b/packages/DocumentsUI/src/com/android/documentsui/dirlist/Model.java
index 49691d416b22..fce16c63979b 100644
--- a/packages/DocumentsUI/src/com/android/documentsui/dirlist/Model.java
+++ b/packages/DocumentsUI/src/com/android/documentsui/dirlist/Model.java
@@ -19,7 +19,6 @@ package com.android.documentsui.dirlist;
 import static com.android.documentsui.Shared.DEBUG;
 import static com.android.documentsui.model.DocumentInfo.getCursorString;
 import static com.android.internal.util.Preconditions.checkNotNull;
-import static com.android.internal.util.Preconditions.checkState;
 
 import android.content.ContentProviderClient;
 import android.content.ContentResolver;
@@ -34,7 +33,6 @@ import android.support.annotation.Nullable;
 import android.support.annotation.VisibleForTesting;
 import android.support.v7.widget.RecyclerView;
 import android.util.Log;
-import android.util.SparseArray;
 
 import com.android.documentsui.BaseActivity.DocumentContext;
 import com.android.documentsui.DirectoryResult;
@@ -42,11 +40,9 @@ import com.android.documentsui.DocumentsApplication;
 import com.android.documentsui.RootCursorWrapper;
 import com.android.documentsui.dirlist.MultiSelectManager.Selection;
 import com.android.documentsui.model.DocumentInfo;
-import com.android.internal.annotations.GuardedBy;
 
 import java.util.ArrayList;
 import java.util.HashMap;
-import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
 
@@ -56,14 +52,9 @@ import java.util.Set;
 @VisibleForTesting
 public class Model implements DocumentContext {
     private static final String TAG = "Model";
-    private RecyclerView.Adapter<?> mViewAdapter;
     private Context mContext;
     private int mCursorCount;
     private boolean mIsLoading;
-    @GuardedBy("mPendingDelete")
-    private Boolean mPendingDelete = false;
-    @GuardedBy("mPendingDelete")
-    private Set<String> mMarkedForDeletion = new HashSet<>();
     private List<UpdateListener> mUpdateListeners = new ArrayList<>();
     @Nullable private Cursor mCursor;
     @Nullable String info;
@@ -72,7 +63,6 @@ public class Model implements DocumentContext {
 
     Model(Context context, RecyclerView.Adapter<?> viewAdapter) {
         mContext = context;
-        mViewAdapter = viewAdapter;
     }
 
     /**
@@ -142,9 +132,7 @@ public class Model implements DocumentContext {
 
     @VisibleForTesting
     int getItemCount() {
-        synchronized(mPendingDelete) {
-            return mCursorCount - mMarkedForDeletion.size();
-        }
+        return mCursorCount;
     }
 
     /**
@@ -197,107 +185,24 @@ public class Model implements DocumentContext {
         return mCursor;
     }
 
-    List<DocumentInfo> getDocumentsMarkedForDeletion() {
-        // TODO(stable-id): This could be just a plain old selection now.
-        synchronized (mPendingDelete) {
-            final int size = mMarkedForDeletion.size();
-            List<DocumentInfo> docs =  new ArrayList<>(size);
-
-            for (String id: mMarkedForDeletion) {
-                Integer position = mPositions.get(id);
-                checkState(position != null);
-                mCursor.moveToPosition(position);
-                final DocumentInfo doc = DocumentInfo.fromDirectoryCursor(mCursor);
-                docs.add(doc);
-            }
-            return docs;
-        }
-    }
-
-    /**
-     * Marks the given files for deletion. This will remove them from the UI. Clients must then
-     * call either {@link #undoDeletion()} or {@link #finalizeDeletion()} to cancel or confirm
-     * the deletion, respectively. Only one deletion operation is allowed at a time.
-     *
-     * @param selected A selection representing the files to delete.
-     */
-    void markForDeletion(Selection selected) {
-        synchronized (mPendingDelete) {
-            mPendingDelete = true;
-            // Only one deletion operation at a time.
-            checkState(mMarkedForDeletion.size() == 0);
-            // There should never be more to delete than what exists.
-            checkState(mCursorCount >= selected.size());
-
-            // Adapter notifications must be sent in reverse order of adapter position.  This is
-            // because each removal causes subsequent item adapter positions to change.
-            SparseArray<String> ids = new SparseArray<>();
-            for (int i = ids.size() - 1; i >= 0; i--) {
-                int pos = ids.keyAt(i);
-                mMarkedForDeletion.add(ids.get(pos));
-                mViewAdapter.notifyItemRemoved(pos);
-                if (DEBUG) Log.d(TAG, "Scheduled " + pos + " for delete.");
-            }
-        }
-    }
-
-    /**
-     * Cancels an ongoing deletion operation. All files currently marked for deletion will be
-     * unmarked, and restored in the UI.  See {@link #markForDeletion(Selection)}.
-     */
-    void undoDeletion() {
-        synchronized (mPendingDelete) {
-            // Iterate over deleted items, temporarily marking them false in the deletion list, and
-            // re-adding them to the UI.
-            for (String id: mMarkedForDeletion) {
-                Integer pos= mPositions.get(id);
-                checkNotNull(pos);
-                mMarkedForDeletion.remove(id);
-                mViewAdapter.notifyItemInserted(pos);
-            }
-            resetDeleteData();
-        }
-    }
-
-    private void resetDeleteData() {
-        synchronized (mPendingDelete) {
-            mPendingDelete = false;
-            mMarkedForDeletion.clear();
-        }
-    }
-
-    /**
-     * Finalizes an ongoing deletion operation. All files currently marked for deletion will be
-     * deleted.  See {@link #markForDeletion(Selection)}.
-     *
-     * @param view The view which will be used to interact with the user (e.g. surfacing
-     * snackbars) for errors, info, etc.
-     */
-    void finalizeDeletion(DeletionListener listener) {
-        synchronized (mPendingDelete) {
-            if (mPendingDelete) {
-                // Necessary to avoid b/25072545. Even when that's resolved, this
-                // is a nice safe thing to day.
-                mPendingDelete = false;
-                final ContentResolver resolver = mContext.getContentResolver();
-                DeleteFilesTask task = new DeleteFilesTask(resolver, listener);
-                task.execute();
-            }
-        }
+    public void delete(Selection selected, DeletionListener listener) {
+        final ContentResolver resolver = mContext.getContentResolver();
+        new DeleteFilesTask(resolver, listener).execute(selected);
     }
 
     /**
      * A Task which collects the DocumentInfo for documents that have been marked for deletion,
      * and actually deletes them.
      */
-    private class DeleteFilesTask extends AsyncTask<Void, Void, List<DocumentInfo>> {
+    private class DeleteFilesTask extends AsyncTask<Selection, Void, Void> {
         private ContentResolver mResolver;
         private DeletionListener mListener;
+        private boolean mHadTrouble;
 
         /**
          * @param resolver A ContentResolver for performing the actual file deletions.
          * @param errorCallback A Runnable that is executed in the event that one or more errors
-         *     occured while copying files.  Execution will occur on the UI thread.
+         *     occurred while copying files.  Execution will occur on the UI thread.
          */
         public DeleteFilesTask(ContentResolver resolver, DeletionListener listener) {
             mResolver = resolver;
@@ -305,17 +210,14 @@ public class Model implements DocumentContext {
         }
 
         @Override
-        protected List<DocumentInfo> doInBackground(Void... params) {
-            return getDocumentsMarkedForDeletion();
-        }
+        protected Void doInBackground(Selection... selected) {
+            List<DocumentInfo> toDelete = getDocuments(selected[0]);
+            mHadTrouble = false;
 
-        @Override
-        protected void onPostExecute(List<DocumentInfo> docs) {
-            boolean hadTrouble = false;
-            for (DocumentInfo doc : docs) {
+            for (DocumentInfo doc : toDelete) {
                 if (!doc.isDeleteSupported()) {
                     Log.w(TAG, doc + " could not be deleted.  Skipping...");
-                    hadTrouble = true;
+                    mHadTrouble = true;
                     continue;
                 }
 
@@ -326,21 +228,25 @@ public class Model implements DocumentContext {
                         mResolver, doc.derivedUri.getAuthority());
                     DocumentsContract.deleteDocument(client, doc.derivedUri);
                 } catch (Exception e) {
-                    Log.w(TAG, "Failed to delete " + doc);
-                    hadTrouble = true;
+                    Log.w(TAG, "Failed to delete " + doc, e);
+                    mHadTrouble = true;
                 } finally {
                     ContentProviderClient.releaseQuietly(client);
                 }
             }
 
-            if (hadTrouble) {
+            return null;
+        }
+
+        @Override
+        protected void onPostExecute(Void _) {
+            if (mHadTrouble) {
                 // TODO show which files failed? b/23720103
                 mListener.onError();
                 if (DEBUG) Log.d(TAG, "Deletion task completed.  Some deletions failed.");
             } else {
                 if (DEBUG) Log.d(TAG, "Deletion task completed successfully.");
             }
-            resetDeleteData();
 
             mListener.onCompletion();
         }
diff --git a/packages/DocumentsUI/src/com/android/documentsui/dirlist/MultiSelectManager.java b/packages/DocumentsUI/src/com/android/documentsui/dirlist/MultiSelectManager.java
index b0bcbcd715af..83c82947626f 100644
--- a/packages/DocumentsUI/src/com/android/documentsui/dirlist/MultiSelectManager.java
+++ b/packages/DocumentsUI/src/com/android/documentsui/dirlist/MultiSelectManager.java
@@ -140,10 +140,21 @@ public final class MultiSelectManager implements View.OnKeyListener {
         mEnvironment.registerDataObserver(
                 new RecyclerView.AdapterDataObserver() {
 
+                    private List<String> mModelIds = new ArrayList<>();
+
                     @Override
                     public void onChanged() {
                         // TODO(stable-id): This is causing b/22765812
                         mSelection.clear();
+
+                        // TODO(stable-id): Improve this. It's currently super-inefficient,
+                        // performing a bunch of lookups and inserting into a List. Maybe just add
+                        // another method to the SelectionEnvironment to just grab the whole list at
+                        // once.
+                        mModelIds.clear();
+                        for (int i = 0; i < mEnvironment.getItemCount(); ++i) {
+                            mModelIds.add(mEnvironment.getModelIdFromAdapterPosition(i));
+                        }
                     }
 
                     @Override
@@ -165,8 +176,9 @@ public final class MultiSelectManager implements View.OnKeyListener {
                         int endPosition = startPosition + itemCount;
                         // Remove any disappeared IDs from the selection.
                         for (int i = startPosition; i < endPosition; i++) {
-                            String id = mEnvironment.getModelIdFromAdapterPosition(i);
+                            String id = mModelIds.get(i);
                             mSelection.remove(id);
+                            mModelIds.remove(i);
                         }
                     }
 
diff --git a/packages/DocumentsUI/tests/src/com/android/documentsui/dirlist/DirectoryFragmentModelTest.java b/packages/DocumentsUI/tests/src/com/android/documentsui/dirlist/DirectoryFragmentModelTest.java
deleted file mode 100644
index ed123b4b26c0..000000000000
--- a/packages/DocumentsUI/tests/src/com/android/documentsui/dirlist/DirectoryFragmentModelTest.java
+++ /dev/null
@@ -1,173 +0,0 @@
-/*
- * Copyright (C) 2015 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.documentsui.dirlist;
-
-import android.content.ContentResolver;
-import android.content.Context;
-import android.content.ContextWrapper;
-import android.database.Cursor;
-import android.database.MatrixCursor;
-import android.provider.DocumentsContract.Document;
-import android.support.v7.widget.RecyclerView;
-import android.test.AndroidTestCase;
-import android.test.mock.MockContentResolver;
-import android.test.suitebuilder.annotation.SmallTest;
-import android.view.ViewGroup;
-
-import com.android.documentsui.DirectoryResult;
-import com.android.documentsui.RootCursorWrapper;
-import com.android.documentsui.model.DocumentInfo;
-
-import java.util.ArrayList;
-import java.util.List;
-
-@SmallTest
-public class DirectoryFragmentModelTest extends AndroidTestCase {
-
-    // Item count must be an even number (see setUp below)
-    private static final int ITEM_COUNT = 10;
-    private static final String[] COLUMNS = new String[]{
-        RootCursorWrapper.COLUMN_AUTHORITY,
-        Document.COLUMN_DOCUMENT_ID
-    };
-    private static Cursor cursor;
-
-    private Context mContext;
-    private Model model;
-
-    public void setUp() {
-        setupTestContext();
-
-        // Make two sets of documents under two different authorities but with identical document
-        // IDs.
-        MatrixCursor c = new MatrixCursor(COLUMNS);
-        for (int i = 0; i < ITEM_COUNT/2; ++i) {
-            MatrixCursor.RowBuilder row0 = c.newRow();
-            row0.add(RootCursorWrapper.COLUMN_AUTHORITY, "authority0");
-            row0.add(Document.COLUMN_DOCUMENT_ID, Integer.toString(i));
-
-            MatrixCursor.RowBuilder row1 = c.newRow();
-            row1.add(RootCursorWrapper.COLUMN_AUTHORITY, "authority1");
-            row1.add(Document.COLUMN_DOCUMENT_ID, Integer.toString(i));
-}
-        cursor = c;
-
-        DirectoryResult r = new DirectoryResult();
-        r.cursor = cursor;
-
-        // Instantiate the model with a dummy view adapter and listener that (for now) do nothing.
-        model = new Model(mContext, new DummyAdapter());
-        model.addUpdateListener(new DummyListener());
-        model.update(r);
-    }
-
-    // Tests that the item count is correct.
-    public void testItemCount() {
-        assertEquals(ITEM_COUNT, model.getItemCount());
-    }
-
-    // Tests that the item count is correct after a deletion.
-    public void testItemCount_WithDeletion() {
-        // Simulate deleting 2 files.
-        delete(2, 4);
-
-        assertEquals(ITEM_COUNT - 2, model.getItemCount());
-    }
-
-    // Tests that the item count is correct after a deletion is undone.
-    public void testItemCount_WithUndoneDeletion() {
-        // Simulate deleting 2 files.
-        delete(0, 3);
-
-        // Undo the deletion
-        model.undoDeletion();
-        assertEquals(ITEM_COUNT, model.getItemCount());
-    }
-
-    // Tests that the right things are marked for deletion.
-    public void testMarkForDeletion() {
-        delete(1, 3);
-
-        List<DocumentInfo> docs = model.getDocumentsMarkedForDeletion();
-        assertEquals(2, docs.size());
-        assertEquals("1", docs.get(0).documentId);
-        assertEquals("3", docs.get(1).documentId);
-    }
-
-    // Tests the base case for Model.getItem.
-    public void testGetItem() {
-        for (int i = 0; i < ITEM_COUNT; ++i) {
-            cursor.moveToPosition(i);
-            Cursor c = model.getItem(Model.createId(cursor));
-            assertEquals(i, c.getPosition());
-        }
-    }
-
-    // Tests that Model.getItem returns the right items after a deletion.
-    public void testGetItem_WithDeletion() {
-        // Simulate deleting 2 files.
-        delete(2, 3);
-
-        List<DocumentInfo> docs = getDocumentInfo(0, 1, 2);
-        assertEquals("0", docs.get(0).documentId);
-        assertEquals("1", docs.get(1).documentId);
-        assertEquals("4", docs.get(2).documentId);
-    }
-
-    // Tests that Model.getItem returns the right items after a deletion is undone.
-    public void testGetItem_WithCancelledDeletion() {
-        delete(0, 1);
-        model.undoDeletion();
-
-        // Test that all documents are accounted for, in the right position.
-        for (int i = 0; i < ITEM_COUNT; ++i) {
-            assertEquals(Integer.toString(i), getDocumentInfo(i).get(0).documentId);
-        }
-    }
-
-    private void setupTestContext() {
-        final MockContentResolver resolver = new MockContentResolver();
-        mContext = new ContextWrapper(getContext()) {
-            @Override
-            public ContentResolver getContentResolver() {
-                return resolver;
-            }
-        };
-    }
-
-    private void delete(int... positions) {
-//        model.markForDeletion(new Selection(positions));
-    }
-
-    private List<DocumentInfo> getDocumentInfo(int... positions) {
-//        return model.getDocuments(new Selection(positions));
-        return new ArrayList<>();
-    }
-
-    private static class DummyListener implements Model.UpdateListener {
-        public void onModelUpdate(Model model) {}
-        public void onModelUpdateFailed(Exception e) {}
-    }
-
-    private static class DummyAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {
-        public int getItemCount() { return 0; }
-        public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {}
-        public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
-            return null;
-        }
-    }
-}
diff --git a/packages/DocumentsUI/tests/src/com/android/documentsui/dirlist/ModelTest.java b/packages/DocumentsUI/tests/src/com/android/documentsui/dirlist/ModelTest.java
new file mode 100644
index 000000000000..96ca0f9b262d
--- /dev/null
+++ b/packages/DocumentsUI/tests/src/com/android/documentsui/dirlist/ModelTest.java
@@ -0,0 +1,210 @@
+/*
+ * Copyright (C) 2015 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.documentsui.dirlist;
+
+import static android.test.MoreAsserts.assertNotEqual;
+
+import android.content.ContentResolver;
+import android.content.Context;
+import android.content.ContextWrapper;
+import android.database.Cursor;
+import android.database.MatrixCursor;
+import android.net.Uri;
+import android.os.Bundle;
+import android.provider.DocumentsContract;
+import android.provider.DocumentsContract.Document;
+import android.support.v7.widget.RecyclerView;
+import android.test.AndroidTestCase;
+import android.test.mock.MockContentProvider;
+import android.test.mock.MockContentResolver;
+import android.test.suitebuilder.annotation.SmallTest;
+import android.view.ViewGroup;
+
+import com.android.documentsui.DirectoryResult;
+import com.android.documentsui.RootCursorWrapper;
+import com.android.documentsui.dirlist.MultiSelectManager.Selection;
+import com.android.documentsui.model.DocumentInfo;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.CountDownLatch;
+
+@SmallTest
+public class ModelTest extends AndroidTestCase {
+
+    private static final int ITEM_COUNT = 10;
+    private static final String AUTHORITY = "test_authority";
+    private static final String[] COLUMNS = new String[]{
+        RootCursorWrapper.COLUMN_AUTHORITY,
+        Document.COLUMN_DOCUMENT_ID,
+        Document.COLUMN_FLAGS
+    };
+    private static Cursor cursor;
+
+    private Context context;
+    private Model model;
+    private TestContentProvider provider;
+
+    public void setUp() {
+        setupTestContext();
+
+        MatrixCursor c = new MatrixCursor(COLUMNS);
+        for (int i = 0; i < ITEM_COUNT; ++i) {
+            MatrixCursor.RowBuilder row = c.newRow();
+            row.add(RootCursorWrapper.COLUMN_AUTHORITY, AUTHORITY);
+            row.add(Document.COLUMN_DOCUMENT_ID, Integer.toString(i));
+            row.add(Document.COLUMN_FLAGS, Document.FLAG_SUPPORTS_DELETE);
+        }
+        cursor = c;
+
+        DirectoryResult r = new DirectoryResult();
+        r.cursor = cursor;
+
+        // Instantiate the model with a dummy view adapter and listener that (for now) do nothing.
+        model = new Model(context, new DummyAdapter());
+        model.addUpdateListener(new DummyListener());
+        model.update(r);
+    }
+
+    // Tests that the item count is correct.
+    public void testItemCount() {
+        assertEquals(ITEM_COUNT, model.getItemCount());
+    }
+
+    // Tests multiple authorities with clashing document IDs.
+    public void testModelIdIsUnique() {
+        MatrixCursor c0 = new MatrixCursor(COLUMNS);
+        MatrixCursor c1 = new MatrixCursor(COLUMNS);
+
+
+        // Make two sets of items with the same IDs, under different authorities.
+        final String AUTHORITY0 = "auth0";
+        final String AUTHORITY1 = "auth1";
+        for (int i = 0; i < ITEM_COUNT; ++i) {
+            MatrixCursor.RowBuilder row0 = c0.newRow();
+            row0.add(RootCursorWrapper.COLUMN_AUTHORITY, AUTHORITY0);
+            row0.add(Document.COLUMN_DOCUMENT_ID, Integer.toString(i));
+
+            MatrixCursor.RowBuilder row1 = c1.newRow();
+            row1.add(RootCursorWrapper.COLUMN_AUTHORITY, AUTHORITY1);
+            row1.add(Document.COLUMN_DOCUMENT_ID, Integer.toString(i));
+        }
+
+        for (int i = 0; i < ITEM_COUNT; ++i) {
+            c0.moveToPosition(i);
+            c1.moveToPosition(i);
+            assertNotEqual(Model.createId(c0), Model.createId(c1));
+        }
+    }
+
+    // Tests the base case for Model.getItem.
+    public void testGetItem() {
+        for (int i = 0; i < ITEM_COUNT; ++i) {
+            cursor.moveToPosition(i);
+            Cursor c = model.getItem(Model.createId(cursor));
+            assertEquals(i, c.getPosition());
+        }
+    }
+
+    // Tests that Model.delete works correctly.
+    public void testDelete() throws Exception {
+        // Simulate deleting 2 files.
+        List<DocumentInfo> docsBefore = getDocumentInfo(2, 3);
+        delete(2, 3);
+
+        provider.assertWasDeleted(docsBefore.get(0));
+        provider.assertWasDeleted(docsBefore.get(1));
+    }
+
+    private void setupTestContext() {
+        final MockContentResolver resolver = new MockContentResolver();
+        context = new ContextWrapper(getContext()) {
+            @Override
+            public ContentResolver getContentResolver() {
+                return resolver;
+            }
+        };
+        provider = new TestContentProvider();
+        resolver.addProvider(AUTHORITY, provider);
+    }
+
+    private Selection positionToSelection(int... positions) {
+        Selection s = new Selection();
+        // Construct a selection of the given positions.
+        for (int p: positions) {
+            cursor.moveToPosition(p);
+            s.add(Model.createId(cursor));
+        }
+        return s;
+    }
+
+    private void delete(int... positions) throws InterruptedException {
+        Selection s = positionToSelection(positions);
+        final CountDownLatch latch = new CountDownLatch(1);
+
+        model.delete(
+                s,
+                new Model.DeletionListener() {
+                    @Override
+                    public void onError() {
+                        latch.countDown();
+                    }
+                    @Override
+                    void onCompletion() {
+                        latch.countDown();
+                    }
+                });
+        latch.await();
+    }
+
+    private List<DocumentInfo> getDocumentInfo(int... positions) {
+        return model.getDocuments(positionToSelection(positions));
+    }
+
+    private static class DummyListener implements Model.UpdateListener {
+        public void onModelUpdate(Model model) {}
+        public void onModelUpdateFailed(Exception e) {}
+    }
+
+    private static class DummyAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {
+        public int getItemCount() { return 0; }
+        public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {}
+        public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
+            return null;
+        }
+    }
+
+    private static class TestContentProvider extends MockContentProvider {
+        List<Uri> mDeleted = new ArrayList<>();
+
+        @Override
+        public Bundle call(String method, String arg, Bundle extras) {
+            // Intercept and log delete method calls.
+            if (DocumentsContract.METHOD_DELETE_DOCUMENT.equals(method)) {
+                final Uri documentUri = extras.getParcelable(DocumentsContract.EXTRA_URI);
+                mDeleted.add(documentUri);
+                return new Bundle();
+            } else {
+                return super.call(method, arg, extras);
+            }
+        }
+
+        public void assertWasDeleted(DocumentInfo doc) {
+            assertTrue(mDeleted.contains(doc.derivedUri));
+        }
+    }
+}