docs/html/training/testing/ui-testing/espresso-testing.jd

page.title=Testing UI for a Single App
page.tags=testing,espresso
trainingnavtop=true

@jd:body

<!-- This is the training bar -->
<div id="tb-wrapper">
<div id="tb">
  <h2>Dependencies and Prerequisites</h2>

        <ul>
          <li>Android 2.2 (API level 8) or higher
          </li>

          <li>
            <a href="{@docRoot}tools/testing-support-library/index.html">Android Testing Support
            Library</a>
          </li>
        </ul>

        <h2>
          This lesson teaches you to
        </h2>

        <ol>
          <li><a href="#setup">Set Up Espresso</a></li>

          <li><a href="#build">Create an Espresso Test Class</a></li>

          <li><a href="#run">Run Espresso Tests on a Device or Emulator</a></li>
        </ol>

        <h2>
          You should also read
        </h2>

        <ul>
           <li><a href="{@docRoot}reference/android/support/test/package-summary.html">
              Espresso API Reference</a></li>
        </ul>

        <h2>
          Try it out
        </h2>

        <ul>
          <li>
            <a href="https://github.com/googlesamples/android-testing"
            class="external-link">Espresso Code Samples</a>
          </li>
          <li><a href="https://www.code-labs.io/codelabs/android-testing/index.html?index=..%2F..%2Findex#0"
            class="external-link">Android Testing Codelab</a></li>
        </ul>
      </div>
</div>

    <p>
      Testing user interactions
      within a single app helps to ensure that users do not
      encounter unexpected results or have a poor
      experience when interacting with your app.
      You should get into the habit of creating
      user interface (UI) tests if you need to verify
      that the UI of your app is functioning correctly.
    </p>

    <p>
      The Espresso testing framework, provided by the
      <a href="{@docRoot}tools/testing-support-library/index.html">Android Testing Support Library</a>,
      provides APIs for writing UI tests to simulate
      user interactions within a
      single target app. Espresso tests can run on
      devices running Android 2.3.3 (API level 10) and
      higher. A key benefit of using Espresso is
      that it provides automatic synchronization of test
      actions with the UI of the app you are testing.
      Espresso detects when the main thread is idle,
      so it is able to run your test commands
      at the appropriate time, improving the reliability of
      your tests. This capability also relieves you
      from having to add any timing workarounds,
      such as {@link java.lang.Thread#sleep(long) Thread.sleep()}
      in your test code.
    </p>

    <p>
      The Espresso testing framework is
      an instrumentation-based API and works with the
      <a href="{@docRoot}reference/android/support/test/runner/AndroidJUnitRunner.html">{@code
      AndroidJUnitRunner}</a> test runner.
    </p>

    <h2 id="setup">
      Set Up Espresso
    </h2>

<p>
  Before building your UI test with Espresso,
  make sure to configure your test source code
  location and project dependencies, as described in
  <a href="{@docRoot}training/testing/start/index.html#config-instrumented-tests">Getting Started with Testing</a>.
</p>

<p>
  In the {@code build.gradle} file of your Android app
  module, you must set a dependency
  reference to the Espresso library:
</p>

<pre>
dependencies {
    // Other dependencies ...
    androidTestCompile 'com.android.support.test.espresso:espresso-core:2.2.2'
}
</pre>

<p>
  Turn off animations on your test device &mdash;
  leaving system animations turned on in the test
  device might cause unexpected results or may
  lead your test to fail. Turn off animations from
  <em>Settings</em> by opening <em>Developer options</em>
  and turning all the following options off:
</p>

<p>
  <ul>
    <li>
      <strong>Window animation scale</strong>
    </li>

    <li>
      <strong>Transition animation scale</strong>
    </li>

    <li>
      <strong>Animator duration scale</strong>
    </li>
  </ul>
</p>

<p>
  If you want to set up your project to use Espresso
  features other than what the core API
  provides, see this
  <a href="https://google.github.io/android-testing-support-library/docs/espresso/index.html"
  class="external-link">resource</a>.</p>

<!-- Section 2 -->

<h2 id="build">
  Create an Espresso Test Class
</h2>

<p>
  To create an Espresso test, create a Java
  class that follows this programming model:
</p>

<ol>
  <li>
    Find the UI component you want to test in
    an {@link android.app.Activity} (for example, a
    sign-in button in the app) by calling the
    <a href="{@docRoot}reference/android/support/test/espresso/Espresso.html#onView(org.hamcrest.Matcher<android.view.View>)">
    {@code onView()}</a> method, or the
    <a href="{@docRoot}reference/android/support/test/espresso/Espresso.html#onData(org.hamcrest.Matcher<java.lang.Object>)">
    {@code onData()}</a> method for {@link android.widget.AdapterView} controls.
  </li>

  <li>
    Simulate a specific user interaction to
    perform on that UI component, by calling the
    <a href="{@docRoot}reference/android/support/test/espresso/ViewInteraction.html#perform(android.support.test.espresso.ViewAction...)">{@code ViewInteraction.perform()}</a>
    or
    <a href="{@docRoot}reference/android/support/test/espresso/DataInteraction.html#perform(android.support.test.espresso.ViewAction...)">{@code DataInteraction.perform()}</a>
    method and passing in the user action
    (for example, click on the sign-in button). To sequence
    multiple actions on the same UI component, chain them using a comma-separated list in your
    method argument.
  </li>

  <li>
    Repeat the steps above as necessary, to simulate a user flow across multiple
    activities in the target app.
  </li>

  <li>
    Use the
    <a href="{@docRoot}reference/android/support/test/espresso/assertion/ViewAssertions.html">{@code ViewAssertions}</a>
    methods to check that the UI reflects the expected
    state or behavior, after these user interactions are performed.
  </li>
</ol>

<p>
  These steps are covered in more detail in the sections below.
</p>

<p>
  The following code snippet shows how your test
  class might invoke this basic workflow:
</p>

<pre>
onView(withId(R.id.my_view))            // withId(R.id.my_view) is a ViewMatcher
        .perform(click())               // click() is a ViewAction
        .check(matches(isDisplayed())); // matches(isDisplayed()) is a ViewAssertion
</pre>

<!-- Section 2.1 -->

<h3 id="espresso-atr">
  Using Espresso with ActivityTestRule
</h3>

<p>
  The following section describes how to create a
  new Espresso test in the JUnit 4 style and use
  <a href="{@docRoot}reference/android/support/test/rule/ActivityTestRule.html">{@code ActivityTestRule}</a>
  to reduce the amount of boilerplate code you need to write. By using
  <a href="{@docRoot}reference/android/support/test/rule/ActivityTestRule.html">{@code ActivityTestRule}</a>,
  the testing framework launches the activity under test
  before each test method annotated with
  <code>&#64;Test</code> and before any method annotated with
  <code>&#64;Before</code>. The framework handles
  shutting down the activity after the test finishes
  and all methods annotated with <code>&#64;After</code> are run.
</p>

<pre>
package com.example.android.testing.espresso.BasicSample;

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

import android.support.test.rule.ActivityTestRule;
import android.support.test.runner.AndroidJUnit4;
...

&#64;RunWith(AndroidJUnit4.class)
&#64;LargeTest
public class ChangeTextBehaviorTest {

    private String mStringToBetyped;

    &#64;Rule
    public ActivityTestRule&lt;MainActivity&gt; mActivityRule = new ActivityTestRule&lt;&gt;(
            MainActivity.class);

    &#64;Before
    public void initValidString() {
        // Specify a valid string.
        mStringToBetyped = "Espresso";
    }

    &#64;Test
    public void changeText_sameActivity() {
        // Type text and then press the button.
        onView(withId(R.id.editTextUserInput))
                .perform(typeText(mStringToBetyped), closeSoftKeyboard());
        onView(withId(R.id.changeTextBt)).perform(click());

        // Check that the text was changed.
        onView(withId(R.id.textToBeChanged))
                .check(matches(withText(mStringToBetyped)));
    }
}
</pre>

<!-- Section 2.2 -->

<h3 id="accessing-ui-components">
  Accessing UI Components
</h3>

<p>
  Before Espresso can interact with the app
  under test, you must first specify the UI component
  or <em>view</em>. Espresso supports the use of
  <a href="http://hamcrest.org/" class="external-link">Hamcrest matchers</a>
  for specifying views and adapters in your app.
</p>

<p>
  To find the view, call the
  <a href="{@docRoot}reference/android/support/test/espresso/Espresso.html#onView(org.hamcrest.Matcher<android.view.View>)">{@code onView()}</a>
  method and pass in a view matcher that
  specifies the view that you are targeting. This is
  described in more detail in
  <a href="#specifying-view-matcher">Specifying a View Matcher</a>.
  The <a href="{@docRoot}reference/android/support/test/espresso/Espresso.html#onView(org.hamcrest.Matcher<android.view.View>)">{@code onView()}</a>
  method returns a
  <a href="{@docRoot}reference/android/support/test/espresso/ViewInteraction.html">{@code ViewInteraction}</a>
  object that allows your test to interact with the view.
  However, calling the
  <a href="{@docRoot}reference/android/support/test/espresso/Espresso.html#onView(org.hamcrest.Matcher<android.view.View>)">
  {@code onView()}</a>
  method may not work if you want to locate a view in
  an {@link android.support.v7.widget.RecyclerView} layout.
  In this case, follow the instructions in
  <a href="#locating-adpeterview-view">Locating a view in an AdapterView</a>
  instead.
</p>

<p class="note">
  <strong>Note</strong>:
  The <a href="{@docRoot}reference/android/support/test/espresso/Espresso.html#onView(org.hamcrest.Matcher<android.view.View>)">{@code onView()}</a>
  method does not check if the view you specified is
  valid. Instead, Espresso searches only the
  current view hierarchy, using the matcher provided.
  If no match is found, the method throws a
  <a href="{@docRoot}reference/android/support/test/espresso/NoMatchingViewException.html">{@code NoMatchingViewException}</a>.
</p>

<p>
  The following code snippet shows how you might write a test that accesses an
  {@link android.widget.EditText} field,
  enters a string of text, closes the virtual keyboard,
  and then performs a button click.
</p>

<pre>
public void testChangeText_sameActivity() {
    // Type text and then press the button.
    onView(withId(R.id.editTextUserInput))
            .perform(typeText(STRING_TO_BE_TYPED), closeSoftKeyboard());
    onView(withId(R.id.changeTextButton)).perform(click());

    // Check that the text was changed.
    ...
}
</pre>

<!-- Section 2.2.1 -->
<h4 id="specifying-view-matcher">
  Specifying a View Matcher
</h4>

<p>
  You can specify a view matcher by using these approaches:
</p>

<ul>
  <li>Calling methods in the
    <a href="{@docRoot}reference/android/support/test/espresso/matcher/ViewMatchers.html">{@code ViewMatchers}</a>
    class. For example, to find a view by looking for a text string it
    displays, you can call a method like this:
<pre>
onView(withText("Sign-in"));
</pre>

    <p>
      Similarly you can call
      <a href="{@docRoot}reference/android/support/test/espresso/matcher/ViewMatchers.html#withId(int)">{@code withId()}</a>
      and providing the resource ID ({@code R.id}) of the view,
      as shown in the
      following example:
    </p>

<pre>
onView(withId(R.id.button_signin));
</pre>

    <p>
      Android resource IDs are not guaranteed to be unique.
      If your test attempts to match to a
      resource ID used by more than one view, Espresso throws an
      <a href="{@docRoot}reference/android/support/test/espresso/AmbiguousViewMatcherException.html">{@code AmbiguousViewMatcherException}</a>.
    </p>
  </li>

  <li>
    Using the Hamcrest
    <a href="http://hamcrest.org/JavaHamcrest/javadoc/1.3/org/hamcrest/Matchers.html"
    class="external-link">{@code Matchers}</a> class. You can use the
    {@code allOf()} methods to combine multiple matchers, such as
    {@code containsString()} and {@code instanceOf()}.
    This approach allows you to
    filter the match results more narrowly, as shown in the following example:

<pre>
onView(allOf(withId(R.id.button_signin), withText("Sign-in")));
</pre>

    <p>
      You can use the {@code not} keyword to filter
      for views that don't correspond to the matcher, as
      shown in the following example:
    </p>

<pre>
onView(allOf(withId(R.id.button_signin), not(withText("Sign-out"))));
</pre>

    <p>
      To use these methods in your test,
      import the {@code org.hamcrest.Matchers} package. To
      learn more about Hamcrest matching, see the
      <a href="http://hamcrest.org/" class="external-link">Hamcrest site</a>.
    </p>
  </li>
</ul>

<p>
  To improve the performance of your Espresso tests,
  specify the minimum matching information
  needed to find your target view. For example,
  if a view is uniquely identifiable by its
  descriptive text, you do not need to specify
  that it is also assignable from the
  {@link android.widget.TextView} instance.
</p>

<!-- Section 2.2.2 -->

<h4 id="#locating-adpeterview-view">
  Locating a view in an AdapterView
</h4>

<p>
  In an {@link android.widget.AdapterView} widget,
  the view is dynamically populated with child
  views at runtime. If the target view you want to test is inside an
  {@link android.widget.AdapterView}
  (such as a {@link android.widget.ListView},
  {@link android.widget.GridView}, or
  {@link android.widget.Spinner}), the
  <a href="{@docRoot}reference/android/support/test/espresso/Espresso.html#onView(org.hamcrest.Matcher<android.view.View>)">{@code onView()}</a>
  method might not work because only a
  subset of the views may be loaded in the current view hierarchy.
</p>

<p>
  Instead, call the
  <a href="{@docRoot}reference/android/support/test/espresso/Espresso.html#onData(org.hamcrest.Matcher<java.lang.Object>)">{@code onData()}</a>
  method to obtain a
  <a href="{@docRoot}reference/android/support/test/espresso/DataInteraction.html">{@code DataInteraction}</a>
  object to access the target view element.
  Espresso handles loading the target view element
  into the current view hierarchy. Espresso
  also takes care of scrolling to the target element,
  and putting the element into focus.
</p>

<p class="note">
  <strong>Note</strong>: The
  <a href="{@docRoot}reference/android/support/test/espresso/Espresso.html#onData(org.hamcrest.Matcher<java.lang.Object>)">{@code onData()}</a>
  method does not check if the item you
  specified corresponds with a view. Espresso searches
  only the current view hierarchy. If no match is found, the method throws a
  <a href="{@docRoot}reference/android/support/test/espresso/NoMatchingViewException.html">{@code NoMatchingViewException}</a>.
</p>

<p>
  The following code snippet shows how you can use the
  <a href="{@docRoot}reference/android/support/test/espresso/Espresso.html#onData(org.hamcrest.Matcher<java.lang.Object>)">{@code onData()}</a>
  method together
  with Hamcrest matching to search for a specific
  row in a list that contains a given string.
  In this example, the {@code LongListActivity} class
  contains a list of strings exposed
  through a {@link android.widget.SimpleAdapter}.
</p>

<pre>
onData(allOf(is(instanceOf(Map.class)),
        hasEntry(equalTo(LongListActivity.ROW_TEXT), is("test input")));
</pre>

<!-- Section 2.3 -->

<h3 id="perform-actions">Performing Actions</h3>

<p>
  Call the
  <a href="{@docRoot}reference/android/support/test/espresso/ViewInteraction.html#perform(android.support.test.espresso.ViewAction...)">{@code ViewInteraction.perform()}</a>
  or
  <a href="{@docRoot}reference/android/support/test/espresso/DataInteraction.html#perform(android.support.test.espresso.ViewAction...)">{@code DataInteraction.perform()}</a>
  methods to
  simulate user interactions on the UI component. You must pass in one or more
  <a href="{@docRoot}reference/android/support/test/espresso/ViewAction.html">{@code ViewAction}</a>
  objects as arguments. Espresso fires each action in sequence according to
  the given order, and executes them in the main thread.
</p>

<p>
  The
  <a href="{@docRoot}reference/android/support/test/espresso/action/ViewActions.html">{@code ViewActions}</a>
  class provides a list of helper methods for specifying common actions.
  You can use these methods as convenient shortcuts
  instead of creating and configuring individual
  <a href="{@docRoot}reference/android/support/test/espresso/ViewAction.html">{@code ViewAction}</a>
  objects. You can specify such actions as:
</p>

<ul>
  <li>
   <a href="{@docRoot}reference/android/support/test/espresso/action/ViewActions.html#click()">{@code ViewActions.click()}</a>:
   Clicks on the view.
  </li>

  <li>
   <a href="{@docRoot}reference/android/support/test/espresso/action/ViewActions.html#typeText(java.lang.String)">{@code ViewActions.typeText()}</a>:
   Clicks on a view and enters a specified string.
  </li>

  <li>
    <a href="{@docRoot}reference/android/support/test/espresso/action/ViewActions.html#scrollTo()">{@code ViewActions.scrollTo()}</a>:
    Scrolls to the view. The
    target view must be subclassed from {@link android.widget.ScrollView}
    and the value of its
    <a href="http://developer.android.com/reference/android/view/View.html#attr_android:visibility">{@code android:visibility}</a>
    property must be {@link android.view.View#VISIBLE}. For views that extend
    {@link android.widget.AdapterView} (for example,
    {@link android.widget.ListView}), the
    <a href="{@docRoot}reference/android/support/test/espresso/Espresso.html#onData(org.hamcrest.Matcher<java.lang.Object>)">{@code onData()}</a>
    method takes care of scrolling for you.
  </li>

  <li>
    <a href="{@docRoot}reference/android/support/test/espresso/action/ViewActions.html#pressKey(int)">{@code ViewActions.pressKey()}</a>:
    Performs a key press using a specified keycode.
  </li>

  <li>
    <a href="{@docRoot}reference/android/support/test/espresso/action/ViewActions.html#clearText()">{@code ViewActions.clearText()}</a>:
  Clears the text in the target view.
  </li>
</ul>

<p>
  If the target view is inside a {@link android.widget.ScrollView},
  perform the
  <a href="{@docRoot}reference/android/support/test/espresso/action/ViewActions.html#scrollTo()">{@code ViewActions.scrollTo()}</a>
  action first to display the view in the screen before other proceeding
  with other actions. The
  <a href="{@docRoot}reference/android/support/test/espresso/action/ViewActions.html#scrollTo()">{@code ViewActions.scrollTo()}</a>
  action will have no effect if the view is already displayed.
</p>

<!-- Section 2.4 -->

<h3 id="intents">
  Test your activities in isolation with Espresso Intents
</h3>

<p>
  <a href="https://google.github.io/android-testing-support-library/docs/espresso/intents/index.html" class="external-link">Espresso Intents</a>
  enables validation and stubbing of intents sent out by an app.
  With Espresso Intents, you can test an app, activity, or service in isolation
  by intercepting outgoing intents, stubbing the result, and sending it back to
  the component under test.
</p>

<p>
  To begin testing with Espresso Intents, you need
  to add the following line to your app's build.gradle file:
</p>

<pre>
dependencies {
  // Other dependencies ...
  androidTestCompile 'com.android.support.test.espresso:espresso-intents:2.2.2'
}
</pre>

<p>
  To test an intent, you need to create an instance of the
  <a href="{@docRoot}reference/android/support/test/espresso/intent/rule/IntentsTestRule.html">IntentsTestRule</a>
  class, which is very similar to the
  <a href="{@docRoot}reference/android/support/test/rule/ActivityTestRule.html">ActivityTestRule</a>
  class.
  The
  <a href="{@docRoot}reference/android/support/test/espresso/intent/rule/IntentsTestRule.html">IntentsTestRule</a>
  class initializes Espresso Intents before each test,
  terminates the host activity,
  and releases Espresso Intents after each test.
</p>

<p>
  The test class shown in the following codes snippet provides a simple
  test for an explicit intent. It tests the activities and intents created in the
  <a href="{@docRoot}training/basics/firstapp/index.html">Building Your First App</a>
  tutorial.
</p>

<pre>
&#64;Large
&#64;RunWith(AndroidJUnit4.class)
public class SimpleIntentTest {

    private static final String MESSAGE = "This is a test";
    private static final String PACKAGE_NAME = "com.example.myfirstapp";

    /* Instantiate an IntentsTestRule object. */
    &#64;Rule
    public IntentsTestRule&lg;MainActivity&gt; mIntentsRule =
      new IntentsTestRule&lg;&gt;(MainActivity.class);

    &#64;Test
    public void verifyMessageSentToMessageActivity() {

        // Types a message into a EditText element.
        onView(withId(R.id.edit_message))
                .perform(typeText(MESSAGE), closeSoftKeyboard());

        // Clicks a button to send the message to another
        // activity through an explicit intent.
        onView(withId(R.id.send_message)).perform(click());

        // Verifies that the DisplayMessageActivity received an intent
        // with the correct package name and message.
        intended(allOf(
                hasComponent(hasShortClassName(".DisplayMessageActivity")),
                toPackage(PACKAGE_NAME),
                hasExtra(MainActivity.EXTRA_MESSAGE, MESSAGE)));

    }
}
</pre>

<p>
  For more information about Espresso Intents, see the
  <a href="https://google.github.io/android-testing-support-library/docs/espresso/intents/index.html"
  class="external-link">Espresso Intents
  documentation on the Android Testing Support Library site</a>.
  You can also download the
  <a href="https://github.com/googlesamples/android-testing/tree/master/ui/espresso/IntentsBasicSample"
  class="external-link">IntentsBasicSample</a> and
  <a href="https://github.com/googlesamples/android-testing/tree/master/ui/espresso/IntentsAdvancedSample"
  class="external-link">IntentsAdvancedSample</a>
  code samples.
</p>

<!-- Section 2.5 -->

<h3 id="webviews">
  Testing WebViews with Espresso Web
</h3>

<p>
  Espresso Web allows you to test {@link android.webkit.WebView} components
  contained within an activity. It uses the
  <a href="http://docs.seleniumhq.org/docs/03_webdriver.jsp"
  class="external-link">WebDriver API</a> to inspect and control the
  behavior of a {@link android.webkit.WebView}.
</p>

<p>
  To begin testing with Espresso Web, you need
  to add the following line to your app's build.gradle file:
</p>

<pre>
dependencies {
  // Other dependencies ...
  androidTestCompile 'com.android.support.test.espresso:espresso-web:2.2.2'
}
</pre>

<p>
  When creating a test using Espresso Web, you need to enable
  JavaScript on the {@link android.webkit.WebView} when you instantiate the
  <a href="{@docRoot}reference/android/support/test/rule/ActivityTestRule.html">ActivityTestRule</a>
  object to test the activity. In the tests, you can select
  HTML elements displayed in the
  {@link android.webkit.WebView} and simulate user interactions, like
  entering text into a text box and then clicking a button. After the actions
  are completed, you can then verify that the results on the
  Web page match the results that you expect.
</p>

<p>
  In the following code snippet, the class tests
  a {@link android.webkit.WebView} component with the id value 'webview'
  in the activity being tested.
  The <code>verifyValidInputYieldsSuccesfulSubmission()</code> test selects an
  <code>&lt;input&gt;</code> element on the
  Web page, enters some text, and checks text that appears in
  another element.
</p>

<pre>
&#64;LargeTest
&#64;RunWith(AndroidJUnit4.class)
public class WebViewActivityTest {

    private static final String MACCHIATO = "Macchiato";
    private static final String DOPPIO = "Doppio";

    &#64;Rule
    public ActivityTestRule<WebViewActivity> mActivityRule =
        new ActivityTestRule<WebViewActivity>(WebViewActivity.class,
            false /* Initial touch mode */, false /*  launch activity */) {

        &#64;Override
        protected void afterActivityLaunched() {
            // Enable JavaScript.
            onWebView().forceJavascriptEnabled();
        }
    }

    &#64;Test
    public void typeTextInInput_clickButton_SubmitsForm() {
       // Lazily launch the Activity with a custom start Intent per test
       mActivityRule.launchActivity(withWebFormIntent());

       // Selects the WebView in your layout.
       // If you have multiple WebViews you can also use a
       // matcher to select a given WebView, onWebView(withId(R.id.web_view)).
       onWebView()
           // Find the input element by ID
           .withElement(findElement(Locator.ID, "text_input"))
           // Clear previous input
           .perform(clearElement())
           // Enter text into the input element
           .perform(DriverAtoms.webKeys(MACCHIATO))
           // Find the submit button
           .withElement(findElement(Locator.ID, "submitBtn"))
           // Simulate a click via JavaScript
           .perform(webClick())
           // Find the response element by ID
           .withElement(findElement(Locator.ID, "response"))
           // Verify that the response page contains the entered text
           .check(webMatches(getText(), containsString(MACCHIATO)));
    }
}
</pre>

<p>
  For more information about Espresso Web, see the
  <a href="https://google.github.io/android-testing-support-library/docs/espresso/web/index.html"
  class="external-link">Espresso
  Web documentation on the Android Testing Support Library site.</a>.
  You can also download this code snippet as part of the
  <a href="https://github.com/googlesamples/android-testing/tree/master/ui/espresso/WebBasicSample"
  class="external-link">Espresso Web code sample</a>.
</p>

<!-- Section 2.6 -->

<h3 id="verify-results">
  Verifying Results
</h3>

<p>
  Call the
  <a href="{@docRoot}reference/android/support/test/espresso/ViewInteraction.html#check(android.support.test.espresso.ViewAssertion)">{@code ViewInteraction.check()}</a>
  or
  <a href="{@docRoot}reference/android/support/test/espresso/DataInteraction.html#check(android.support.test.espresso.ViewAssertion)">{@code DataInteraction.check()}</a>
  method to assert
  that the view in the UI matches some expected state. You must pass in a
  <a href="{@docRoot}reference/android/support/test/espresso/ViewAssertion.html">{@code ViewAssertion}</a>
  object as the argument. If the assertion fails, Espresso throws
  an {@link junit.framework.AssertionFailedError}.
</p>

<p>
  The
  <a href="{@docRoot}reference/android/support/test/espresso/assertion/ViewAssertions.html">{@code ViewAssertions}</a>
  class provides a list of helper methods for specifying common
  assertions. The assertions you can use include:
</p>

<ul>
  <li>
    <a href="{@docRoot}reference/android/support/test/espresso/assertion/ViewAssertions.html#doesNotExist()">{@code doesNotExist}</a>:
    Asserts that there is no view matching the specified
    criteria in the current view hierarchy.
  </li>

  <li>
    <a href="{@docRoot}reference/android/support/test/espresso/assertion/ViewAssertions.html#matches(org.hamcrest.Matcher&lt;? super android.view.View&gt;)">{@code matches}</a>:
    Asserts that the specified view exists in the current view hierarchy
    and its state matches some given Hamcrest matcher.
  </li>

  <li>
    <a href="{@docRoot}reference/android/support/test/espresso/assertion/ViewAssertions.html#selectedDescendantsMatch(org.hamcrest.Matcher&lt;android.view.View&gt;, org.hamcrest.Matcher&lt;android.view.View&gt;)">{@code selectedDescendentsMatch}</a>:
    Asserts that the specified children views for a
    parent view exist, and their state matches some given Hamcrest matcher.
  </li>
</ul>

<p>
  The following code snippet shows how you might
  check that the text displayed in the UI has
  the same value as the text previously entered in the
  {@link android.widget.EditText} field.
</p>

<pre>
public void testChangeText_sameActivity() {
    // Type text and then press the button.
    ...

    // Check that the text was changed.
    onView(withId(R.id.textToBeChanged))
            .check(matches(withText(STRING_TO_BE_TYPED)));
}
</pre>

<!-- Section 3 -->

<h2 id="run">
  Run Espresso Tests on a Device or Emulator
</h2>

<p>
  You can run Espresso tests from
  <a href="{@docRoot}studio/index.html">Android Studio</a> or
  from the command-line. Make sure to specify
  <a href="{@docRoot}reference/android/support/test/runner/AndroidJUnitRunner.html">{@code AndroidJUnitRunner}</a>
  as the default instrumentation runner in your project.
</p>

<p>
  To run your Espresso test, follow the steps for running instrumented tests
  described in
  <a href="{@docRoot}training/testing/start/index.html#run-instrumented-tests">Getting Started with Testing</a>.
</p>