diff --git a/app/build.gradle b/app/build.gradle
index 91d201b..89a014d 100644
--- a/app/build.gradle
+++ b/app/build.gradle
@@ -12,6 +12,8 @@
         targetSdkVersion 23
         versionCode 1
         versionName "1.0"
+
+        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
     }
     productFlavors {
         firebase {
@@ -20,6 +22,9 @@
         syncbase {
             applicationId "io.v.todos.syncbase"
         }
+        mock {
+            applicationId "io.v.todos.mock"
+        }
     }
     buildTypes {
         release {
@@ -39,15 +44,36 @@
 dependencies {
     compile fileTree(dir: 'libs', include: ['*.jar'])
     testCompile 'junit:junit:4.12'
+
+    // Additional testing libraries (mockito and espresso) for the mock flavor.
+    androidTestMockCompile (
+            'org.mockito:mockito-core:1.10.19',
+            'com.google.dexmaker:dexmaker:1.2',
+            'com.google.dexmaker:dexmaker-mockito:1.2'
+    )
+
+    androidTestMockCompile ('com.android.support.test.espresso:espresso-intents:2.2') {
+            // Necessary to avoid version conflicts
+            exclude group: 'com.android.support', module: 'appcompat'
+            exclude group: 'com.android.support', module: 'support-v4'
+            exclude group: 'com.android.support', module: 'support-annotations'
+            exclude module: 'recyclerview-v7'
+    }
+    androidTestMockCompile('com.android.support.test.espresso:espresso-contrib:2.2') {
+            // Necessary to avoid version conflicts
+            exclude group: 'com.android.support', module: 'appcompat'
+            exclude group: 'com.android.support', module: 'support-v4'
+            exclude group: 'com.android.support', module: 'support-annotations'
+            exclude module: 'recyclerview-v7'
+    }
+
     compile (
             'com.android.support:appcompat-v7:23.1.1',
             'com.android.support:design:23.1.1',
             'com.android.support:cardview-v7:23.1.1',
-            'com.android.support:recyclerview-v7:23.1.1'
-    )
-    firebaseCompile(
-            'com.firebase:firebase-client-android:2.5.2',
+            'com.android.support:recyclerview-v7:23.1.1',
             'com.google.guava:guava:19.0'
     )
+    firebaseCompile 'com.firebase:firebase-client-android:2.5.2'
     syncbaseCompile 'io.v:vanadium-android:2.0'
 }
diff --git a/app/src/androidTestMock/java/io/v/todos/MainActivityTest.java b/app/src/androidTestMock/java/io/v/todos/MainActivityTest.java
new file mode 100644
index 0000000..b2a5497
--- /dev/null
+++ b/app/src/androidTestMock/java/io/v/todos/MainActivityTest.java
@@ -0,0 +1,304 @@
+// Copyright 2016 The Vanadium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package io.v.todos;
+
+import android.content.DialogInterface;
+import android.support.test.espresso.contrib.RecyclerViewActions;
+import android.support.test.espresso.intent.Intents;
+import android.support.v7.app.AlertDialog;
+import android.support.v7.widget.RecyclerView;
+import android.test.ActivityInstrumentationTestCase2;
+import android.widget.EditText;
+
+import io.v.todos.model.ListMetadata;
+import io.v.todos.model.ListSpec;
+import io.v.todos.persistence.ListEventListener;
+import io.v.todos.persistence.MainPersistence;
+
+import static android.support.test.espresso.Espresso.onView;
+import static android.support.test.espresso.action.ViewActions.click;
+import static android.support.test.espresso.action.ViewActions.swipeLeft;
+import static android.support.test.espresso.action.ViewActions.swipeRight;
+import static android.support.test.espresso.assertion.ViewAssertions.matches;
+import static android.support.test.espresso.intent.Intents.intended;
+import static android.support.test.espresso.intent.matcher.IntentMatchers.hasComponent;
+import static android.support.test.espresso.matcher.ViewMatchers.hasDescendant;
+import static android.support.test.espresso.matcher.ViewMatchers.withId;
+import static android.support.test.espresso.matcher.ViewMatchers.withText;
+import static org.hamcrest.Matchers.not;
+import static org.mockito.Matchers.any;
+import static org.mockito.Matchers.anyString;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.never;
+import static org.mockito.Mockito.verify;
+
+/**
+ * Contains UI tests for the MainActivity that isolate the MainPersistence's behavior.
+ * <p/>
+ * Note: These tests will fail if the device's screen is off.
+ * TODO(alexfandrianto): There do seem to be ways to force the screen to turn on though.
+ * <p/>
+ * Most sleeps are present in order to make the tests easier to follow when running.
+ * <p/>
+ * Created by alexfandrianto on 4/21/16.
+ */
+public class MainActivityTest extends ActivityInstrumentationTestCase2<MainActivity> {
+    private static final String KEY1 = "asdlkjweriousdf";
+    private static final String KEY2 = "woeiuflskjeroius";
+    private static final String NAME1 = "weoislkjdflkejroif";
+    private static final String NAME2 = "weurlksdnoielrkmlsd";
+    private static final String NAME3 = "oisdlkwejrllisdfelkejr";
+    private static final long UI_DELAY = 500; // Tweak this value to adjust the test speed.
+
+    private MainActivity mActivity;
+
+    public MainActivityTest() {
+        super(MainActivity.class);
+    }
+
+    @Override
+    protected void setUp() throws Exception {
+        super.setUp();
+
+        // Certain methods must be called before getActivity. Surprise!
+        setActivityInitialTouchMode(true);
+
+        mActivity = getActivity();
+    }
+
+    @Override
+    protected void tearDown() throws Exception {
+        super.tearDown();
+
+        if (mActivity != null) {
+            mActivity.finish();
+            mActivity = null;
+        }
+    }
+
+    private void pause() {
+        try {
+            Thread.sleep(UI_DELAY);
+        } catch (InterruptedException e) {
+            e.printStackTrace();
+        }
+    }
+
+    private MainPersistence mockPersistence() {
+        MainPersistence mocked = mock(MainPersistence.class);
+        mActivity.setMainPersistence(mocked);
+        return mocked;
+    }
+
+    private AlertDialog beginAddItem() {
+        onView(withId(R.id.fab)).perform(click());
+        pause();
+
+        final AlertDialog dialog = UIUtil.getLastDialog();
+
+        assertTrue(dialog.isShowing());
+
+        mActivity.runOnUiThread(new Runnable() {
+            public void run() {
+                EditText et = (EditText) dialog.getCurrentFocus();
+                et.setText("HELLO WORLD!");
+            }
+        });
+
+        pause();
+
+        return dialog;
+    }
+
+    // Press the fab to attempt to add an item.
+    public void testAttemptAddItem() {
+        MainPersistence mocked = mockPersistence();
+        AlertDialog dialog = beginAddItem();
+
+        dialog.getButton(DialogInterface.BUTTON_POSITIVE).callOnClick();
+
+        pause();
+
+        assertFalse(dialog.isShowing());
+
+        verify(mocked).addTodoList(any(ListSpec.class));
+        verify(mocked, never()).deleteTodoList(anyString());
+        verify(mocked, never()).completeAllTasks(any(ListMetadata.class));
+    }
+
+    // Press the fab but don't actually add the item.
+    public void testAttemptAddItemFail() {
+        MainPersistence mocked = mockPersistence();
+        AlertDialog dialog = beginAddItem();
+
+        dialog.getButton(DialogInterface.BUTTON_NEGATIVE).callOnClick();
+
+        pause();
+
+        assertFalse(dialog.isShowing());
+
+        verify(mocked, never()).addTodoList(any(ListSpec.class));
+        verify(mocked, never()).deleteTodoList(anyString());
+        verify(mocked, never()).completeAllTasks(any(ListMetadata.class));
+    }
+
+    // Press the fab but don't actually add the item.
+    public void testAttemptAddItemCancel() {
+        MainPersistence mocked = mockPersistence();
+        AlertDialog dialog = beginAddItem();
+
+        dialog.dismiss();
+
+        pause();
+
+        assertFalse(dialog.isShowing());
+
+        verify(mocked, never()).addTodoList(any(ListSpec.class));
+        verify(mocked, never()).deleteTodoList(anyString());
+        verify(mocked, never()).completeAllTasks(any(ListMetadata.class));
+    }
+
+    // Add some default items so that we can interact with them with swipes.
+    private void addInitialData() {
+        mActivity.runOnUiThread(new Runnable() {
+            public void run() {
+                ListEventListener<ListMetadata> listener = mActivity.createMainListener();
+                listener.onItemAdd(new ListMetadata(KEY1, NAME1, 0, 0, 0));
+                listener.onItemAdd(new ListMetadata(KEY2, NAME2, 1, 1, 2));
+            }
+        });
+    }
+
+    // Call the listener directly to add an item.
+    public void testDirectlyAddItem() {
+        final ListEventListener<ListMetadata> listener = mActivity.createMainListener();
+
+        RecyclerView recycler = (RecyclerView) mActivity.findViewById(R.id.recycler);
+        pause();
+
+        final ListMetadata data = new ListMetadata(KEY1, NAME1, 0, 0, 0);
+        mActivity.runOnUiThread(new Runnable() {
+            public void run() {
+                listener.onItemAdd(data);
+            }
+        });
+
+        pause();
+        assertEquals(recycler.getAdapter().getItemCount(), 1);
+
+        final ListMetadata data2 = new ListMetadata(KEY2, NAME2, 1, 1, 2);
+        mActivity.runOnUiThread(new Runnable() {
+            public void run() {
+                listener.onItemAdd(data2);
+            }
+        });
+
+        pause();
+        assertEquals(recycler.getAdapter().getItemCount(), 2);
+    }
+
+    public void testDirectlyEditItem() {
+        addInitialData();
+
+        pause();
+
+        RecyclerView recycler = (RecyclerView) mActivity.findViewById(R.id.recycler);
+
+        onView(withId(R.id.recycler)).check(matches(hasDescendant(withText(NAME1))));
+        onView(withId(R.id.recycler)).check(matches(hasDescendant(withText(NAME2))));
+        onView(withId(R.id.recycler)).check(matches(not(hasDescendant(withText(NAME3)))));
+
+        final ListEventListener<ListMetadata> listener = mActivity.createMainListener();
+        mActivity.runOnUiThread(new Runnable() {
+            public void run() {
+                listener.onItemUpdate(new ListMetadata(KEY1, NAME3, 2, 0, 0));
+            }
+        });
+
+        pause();
+
+        onView(withId(R.id.recycler)).check(matches(not(hasDescendant(withText(NAME1)))));
+        onView(withId(R.id.recycler)).check(matches(hasDescendant(withText(NAME2))));
+        onView(withId(R.id.recycler)).check(matches(hasDescendant(withText(NAME3))));
+        assertEquals(recycler.getAdapter().getItemCount(), 2);
+    }
+
+    public void testDirectlyDeleteItem() {
+        addInitialData();
+
+        pause();
+
+        RecyclerView recycler = (RecyclerView) mActivity.findViewById(R.id.recycler);
+
+        onView(withId(R.id.recycler)).check(matches(hasDescendant(withText(NAME1))));
+        onView(withId(R.id.recycler)).check(matches(hasDescendant(withText(NAME2))));
+        onView(withId(R.id.recycler)).check(matches(not(hasDescendant(withText(NAME3)))));
+
+        final ListEventListener<ListMetadata> listener = mActivity.createMainListener();
+        mActivity.runOnUiThread(new Runnable() {
+            public void run() {
+                listener.onItemDelete(KEY2);
+            }
+        });
+
+        pause();
+
+        onView(withId(R.id.recycler)).check(matches(hasDescendant(withText(NAME1))));
+        onView(withId(R.id.recycler)).check(matches(not(hasDescendant(withText(NAME2)))));
+        onView(withId(R.id.recycler)).check(matches(not(hasDescendant(withText(NAME3)))));
+        assertEquals(recycler.getAdapter().getItemCount(), 1);
+    }
+
+    // Swipe a todo list item to the right to mark all of its children as done.
+    public void testAttemptCompleteAllTasks() {
+        MainPersistence mocked = mockPersistence();
+        addInitialData();
+
+        pause();
+
+        // DO UI INTERACTION
+        onView(withId(R.id.recycler)).perform(RecyclerViewActions.actionOnItemAtPosition(1, swipeRight()));
+
+        pause();
+
+        verify(mocked, never()).addTodoList(any(ListSpec.class));
+        verify(mocked, never()).deleteTodoList(anyString());
+        verify(mocked).completeAllTasks(any(ListMetadata.class));
+    }
+
+    // Swipe a todo list item to the left to attempt to delete it.
+    public void testAttemptDeleteItem() {
+        MainPersistence mocked = mockPersistence();
+        addInitialData();
+
+        pause();
+
+        // DO UI INTERACTION
+        onView(withId(R.id.recycler)).perform(RecyclerViewActions.actionOnItemAtPosition(1, swipeLeft()));
+
+        pause();
+
+        verify(mocked, never()).addTodoList(any(ListSpec.class));
+        verify(mocked).deleteTodoList(anyString());
+        verify(mocked, never()).completeAllTasks(any(ListMetadata.class));
+    }
+
+    // Tap a todo list item to launch its corresponding TodoListActivity
+    public void testTapItem() {
+        Intents.init();
+        addInitialData();
+
+        pause();
+
+        // DO UI INTERACTION
+        onView(withId(R.id.recycler)).perform(RecyclerViewActions.actionOnItemAtPosition(1, click()));
+
+        pause();
+
+        // Confirm that the TodoListActivity was started!
+        intended(hasComponent(TodoListActivity.class.getName()));
+        Intents.release();
+    }
+}
diff --git a/app/src/main/java/io/v/todos/MainActivity.java b/app/src/main/java/io/v/todos/MainActivity.java
index 4d39028..8c1e5e3 100644
--- a/app/src/main/java/io/v/todos/MainActivity.java
+++ b/app/src/main/java/io/v/todos/MainActivity.java
@@ -7,6 +7,7 @@
 import android.app.Activity;
 import android.content.Intent;
 import android.os.Bundle;
+import android.support.annotation.VisibleForTesting;
 import android.support.v7.widget.RecyclerView;
 import android.support.v7.widget.helper.ItemTouchHelper;
 import android.view.Menu;
@@ -40,7 +41,7 @@
     // These todos are backed up at the SNACKOOS child of the Firebase URL.
     // We use the snackoosList to track a custom sorted list of the stored values.
     static final String INTENT_SNACKOO_KEY = "snackoo key";
-    private DataList<ListMetadata> snackoosList = new DataList<ListMetadata>();
+    private DataList<ListMetadata> snackoosList = new DataList<>();
 
     // This adapter handle mirrors the firebase list values and generates the corresponding todo
     // item View children for a list view.
@@ -107,32 +108,7 @@
             @Override
             protected MainPersistence initPersistence() throws Exception {
                 return PersistenceFactory.getMainPersistence(mActivity,
-                        new ListEventListener<ListMetadata>() {
-                            @Override
-                            public void onItemAdd(ListMetadata item) {
-                                int position = snackoosList.insertInOrder(item);
-
-                                adapter.notifyItemInserted(position);
-                                setEmptyVisiblity();
-                            }
-
-                            @Override
-                            public void onItemUpdate(ListMetadata item) {
-                                int start = snackoosList.findIndexByKey(item.key);
-                                int end = snackoosList.updateInOrder(item);
-
-                                adapter.notifyItemMoved(start, end);
-                                adapter.notifyItemChanged(end);
-                            }
-
-                            @Override
-                            public void onItemDelete(String key) {
-                                int position = snackoosList.removeByKey(key);
-
-                                adapter.notifyItemRemoved(position);
-                                setEmptyVisiblity();
-                            }
-                        });
+                        createMainListener());
             }
 
             @Override
@@ -142,6 +118,44 @@
         }.execute(PersistenceFactory.mightGetMainPersistenceBlock());
     }
 
+    // Creates a listener for this activity. Visible to tests to allow them to invoke the listener
+    // methods directly.
+    @VisibleForTesting
+    ListEventListener<ListMetadata> createMainListener() {
+        return new ListEventListener<ListMetadata>() {
+            @Override
+            public void onItemAdd(ListMetadata item) {
+                int position = snackoosList.insertInOrder(item);
+
+                adapter.notifyItemInserted(position);
+                setEmptyVisiblity();
+            }
+
+            @Override
+            public void onItemUpdate(ListMetadata item) {
+                int start = snackoosList.findIndexByKey(item.key);
+                int end = snackoosList.updateInOrder(item);
+
+                adapter.notifyItemMoved(start, end);
+                adapter.notifyItemChanged(end);
+            }
+
+            @Override
+            public void onItemDelete(String key) {
+                int position = snackoosList.removeByKey(key);
+
+                adapter.notifyItemRemoved(position);
+                setEmptyVisiblity();
+            }
+        };
+    }
+
+    // Allow the tests to mock out the main persistence.
+    @VisibleForTesting
+    void setMainPersistence(MainPersistence p) {
+        mPersistence = p;
+    }
+
     // Set the visibility based on what the adapter thinks is the visible item count.
     private void setEmptyVisiblity() {
         View v = findViewById(R.id.empty);
diff --git a/app/src/main/java/io/v/todos/UIUtil.java b/app/src/main/java/io/v/todos/UIUtil.java
index d17b822..779d093 100644
--- a/app/src/main/java/io/v/todos/UIUtil.java
+++ b/app/src/main/java/io/v/todos/UIUtil.java
@@ -19,6 +19,11 @@
         return prefix + ": " + DateUtils.getRelativeTimeSpanString(startTime);
     }
 
+    private static AlertDialog lastDialog;
+    public static AlertDialog getLastDialog() {
+        return lastDialog;
+    }
+
     public static void showAddDialog(Context context, String title,
                                      final DialogResponseListener addListener) {
         final EditText todoItem = new EditText(context);
@@ -37,6 +42,7 @@
                 }).show();
         dialog.getWindow().setSoftInputMode(
                 WindowManager.LayoutParams.SOFT_INPUT_STATE_ALWAYS_VISIBLE);
+        lastDialog = dialog;
     }
 
     public static void showEditDialog(Context context, String title, String defaultValue,
@@ -63,6 +69,7 @@
                 }).show();
         dialog.getWindow().setSoftInputMode(
                 WindowManager.LayoutParams.SOFT_INPUT_STATE_ALWAYS_VISIBLE);
+        lastDialog = dialog;
     }
 
     public static abstract class DialogResponseListener {
diff --git a/app/src/main/res/layout/content_main.xml b/app/src/main/res/layout/content_main.xml
index db458e2..f1a47c2 100644
--- a/app/src/main/res/layout/content_main.xml
+++ b/app/src/main/res/layout/content_main.xml
@@ -27,7 +27,7 @@
             android:background="#FF0000"
             android:text="No data"/>
     </LinearLayout>
-    <android.support.design.widget.FloatingActionButton
+    <android.support.design.widget.FloatingActionButton android:id="@+id/fab"
         android:layout_height="wrap_content"
         android:layout_width="wrap_content"
         android:layout_alignParentBottom="true"
diff --git a/app/src/mock/java/io/v/todos/persistence/PersistenceFactory.java b/app/src/mock/java/io/v/todos/persistence/PersistenceFactory.java
new file mode 100644
index 0000000..d6fe975
--- /dev/null
+++ b/app/src/mock/java/io/v/todos/persistence/PersistenceFactory.java
@@ -0,0 +1,87 @@
+// Copyright 2016 The Vanadium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package io.v.todos.persistence;
+
+import android.app.Activity;
+import android.content.Context;
+
+import io.v.todos.model.ListMetadata;
+import io.v.todos.model.ListSpec;
+import io.v.todos.model.Task;
+import io.v.todos.model.TaskSpec;
+
+public final class PersistenceFactory {
+    private PersistenceFactory(){}
+
+    /**
+     * Indicates whether {@link #getMainPersistence(Activity, ListEventListener)} may block. This
+     * can affect whether a progress indicator is shown and whether a worker thread is used.
+     */
+    public static boolean mightGetMainPersistenceBlock() {
+        return false;
+    }
+
+    /**
+     * Instantiates a persistence object that can be used to manipulate todo lists.
+     */
+    public static MainPersistence getMainPersistence(Activity activity,
+                                                     ListEventListener<ListMetadata> listener) {
+        return new MockMainPersistence();
+    }
+
+    /**
+     * Indicates whether {@link #getTodoListPersistence(Activity, String, TodoListListener)} may
+     * block. This can affect whether a progress indicator is shown and whether a worker thread is
+     * used.
+     */
+    public static boolean mightGetTodoListPersistenceBlock() {
+        return false;
+    }
+
+    /**
+     * Instantiates a persistence object that can be used to manipulate a todo list.
+     */
+    public static TodoListPersistence getTodoListPersistence(Activity activity, String key,
+                                                             TodoListListener listener) {
+        return new MockTodoListPersistence();
+    }
+
+    static class MockMainPersistence implements MainPersistence {
+        @Override
+        public void addTodoList(ListSpec listSpec) {}
+
+        @Override
+        public void deleteTodoList(String key) {}
+
+        @Override
+        public void completeAllTasks(ListMetadata listMetadata) {}
+
+        @Override
+        public void close() {}
+    }
+
+    static class MockTodoListPersistence implements TodoListPersistence {
+        @Override
+        public void updateTodoList(ListSpec listSpec) {}
+
+        @Override
+        public void deleteTodoList() {}
+
+        @Override
+        public void addTask(TaskSpec task) {}
+
+        @Override
+        public void updateTask(Task task) {}
+
+        @Override
+        public void deleteTask(String key) {}
+
+        @Override
+        public void setShowDone(boolean showDone) {}
+
+        @Override
+        public void close() {}
+    }
+}
diff --git a/app/src/test/java/io/v/todos/DataListTest.java b/app/src/test/java/io/v/todos/DataListTest.java
new file mode 100644
index 0000000..b8f5512
--- /dev/null
+++ b/app/src/test/java/io/v/todos/DataListTest.java
@@ -0,0 +1,89 @@
+// Copyright 2016 The Vanadium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package io.v.todos;
+
+import org.junit.Test;
+
+import io.v.todos.model.DataList;
+import io.v.todos.model.KeyedData;
+
+import static org.junit.Assert.assertEquals;
+
+/**
+ * A unit test for the DataList. Confirms that keyed data is inserted in the correct order.
+ */
+public class DataListTest {
+    @Test
+    public void dataListTest() throws Exception {
+        DataList<TestKeyedData> dataList = new DataList<>();
+
+        // Insert a few.
+        assertEquals(0, dataList.insertInOrder(new TestKeyedData("b")));
+        assertEquals(1, dataList.insertInOrder(new TestKeyedData("d")));
+        assertEquals(0, dataList.insertInOrder(new TestKeyedData("a")));
+        assertEquals(2, dataList.insertInOrder(new TestKeyedData("c")));
+        assertEquals(0, dataList.insertInOrder(new TestKeyedData("e", -1)));
+        assertEquals(5, dataList.insertInOrder(new TestKeyedData("g", 1)));
+        assertEquals(5, dataList.insertInOrder(new TestKeyedData("f", 1)));
+
+        // We should be at e, a, b, c, d, f, g now.
+        assertEquals(1, dataList.findIndexByKey("a"));
+        assertEquals(2, dataList.findIndexByKey("b"));
+        assertEquals(3, dataList.findIndexByKey("c"));
+        assertEquals(4, dataList.findIndexByKey("d"));
+        assertEquals(0, dataList.findIndexByKey("e"));
+        assertEquals(5, dataList.findIndexByKey("f"));
+        assertEquals(6, dataList.findIndexByKey("g"));
+        assertEquals(-1, dataList.findIndexByKey("h"));
+
+        // Update a few.
+        assertEquals(6, dataList.updateInOrder(new TestKeyedData("b", 2))); // Move b to the back.
+        assertEquals(5, dataList.updateInOrder(new TestKeyedData("a", 2))); // Move a too.
+
+        // Confirm priorities. We should be at e, c, d, f, g, a, b now.
+        assertEquals(2, dataList.findByKey("a").priority);
+        assertEquals(2, dataList.findByKey("b").priority);
+        assertEquals(0, dataList.findByKey("c").priority);
+        assertEquals(0, dataList.findByKey("d").priority);
+        assertEquals(-1, dataList.findByKey("e").priority);
+        assertEquals(1, dataList.findByKey("f").priority);
+        assertEquals(1, dataList.findByKey("g").priority);
+
+        // And now, remove a few.
+        assertEquals(1, dataList.removeByKey("c"));
+        assertEquals(4, dataList.removeByKey("a"));
+
+        // Confirm indexes. e, d, f, g, b
+        assertEquals(-1, dataList.findIndexByKey("a"));
+        assertEquals(4, dataList.findIndexByKey("b"));
+        assertEquals(-1, dataList.findIndexByKey("c"));
+        assertEquals(1, dataList.findIndexByKey("d"));
+        assertEquals(0, dataList.findIndexByKey("e"));
+        assertEquals(2, dataList.findIndexByKey("f"));
+        assertEquals(3, dataList.findIndexByKey("g"));
+        assertEquals(-1, dataList.findIndexByKey("h"));
+    }
+
+    private class TestKeyedData extends KeyedData<TestKeyedData> {
+        int priority;
+
+        TestKeyedData(String key) {
+            super(key);
+        }
+
+        TestKeyedData(String key, int priority) {
+            super(key);
+            this.priority = priority;
+        }
+
+        @Override
+        public int compareTo(TestKeyedData testKeyedData) {
+            if (priority != testKeyedData.priority) {
+                return priority - testKeyedData.priority;
+            }
+            return key.compareTo(testKeyedData.key);
+        }
+    }
+}
\ No newline at end of file
diff --git a/app/src/test/java/io/v/todos/ExampleUnitTest.java b/app/src/test/java/io/v/todos/ExampleUnitTest.java
deleted file mode 100644
index 07340b3..0000000
--- a/app/src/test/java/io/v/todos/ExampleUnitTest.java
+++ /dev/null
@@ -1,19 +0,0 @@
-// Copyright 2016 The Vanadium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-package io.v.todos;
-
-import org.junit.Test;
-
-import static org.junit.Assert.*;
-
-/**
- * To work on unit tests, switch the Test Artifact in the Build Variants view.
- */
-public class ExampleUnitTest {
-    @Test
-    public void addition_isCorrect() throws Exception {
-        assertEquals(4, 2 + 2);
-    }
-}
\ No newline at end of file