Unit and Functional Tests

Debug and secure your Android applications with Android Studio

In this article by Belén Cruz Zapata and Antonio Hernández Niñirola, authors of the book Testing and Securing Android Studio Applications, you will learn how to use unit tests that allow developers to quickly verify the state and behavior of an activity on its own.

(For more resources related to this topic, see here.)

Testing activities

There are two possible modes of testing activities:

  • Functional testing: In functional testing, the activity being tested is created using the system infrastructure. The test code can communicate with the Android system, send events to the UI, or launch another activity.

  • Unit testing: In unit testing, the activity being tested is created with minimal connection to the system infrastructure. The activity is tested in isolation.

In this article, we will explore the Android testing API to learn about the classes and methods that will help you test the activities of your application.

The test case classes

The Android testing API is based on JUnit. Android JUnit extensions are included in the android.test package. The following figure presents the main classes that are involved when testing activities:

Let's learn more about these classes:

  • TestCase: This JUnit class belongs to the junit.framework. The TestCase package represents a general test case. This class is extended by the Android API.

  • InstrumentationTestCase: This class and its subclasses belong to the android.test package. It represents a test case that has access to instrumentation.

  • ActivityTestCase: This class is used to test activities, but for more useful classes, you should use one of its subclasses instead of the main class.

  • ActivityInstrumentationTestCase2: This class provides functional testing of an activity and is parameterized with the activity under test. For example, to evaluate your MainActivity, you have to create a test class named MainActivityTest that extends the ActivityInstrumentationTestCase2 class, shown as follows:

    public class MainActivityTest extends ActivityInstrumentationTestCase2<MainActivity> 
  • ActivityUnitTestCase: This class provides unit testing of an activity and is parameterized with the activity under test. For example, to evaluate your MainActivity, you can create a test class named MainActivityUnitTest that extends the ActivityUnitTestCase class, shown as follows:

    public class MainActivityUnitTest extends ActivityUnitTestCase<MainActivity>

There is a new term that has emerged from the previous classes called Instrumentation.


The execution of an application is ruled by the life cycle, which is determined by the Android system. For example, the life cycle of an activity is controlled by the invocation of some methods: onCreate(), onResume(), onDestroy(), and so on. These methods are called by the Android system and your code cannot invoke them, except while testing. The mechanism to allow your test code to invoke callback methods is known as Android instrumentation.

Android instrumentation is a set of methods to control a component independent of its normal lifecycle. To invoke the callback methods from your test code, you have to use the classes that are instrumented. For example, to start the activity under test, you can use the getActivity() method that returns the activity instance. For each test method invocation, the activity will not be created until the first time this method is called. Instrumentation is necessary to test activities considering the lifecycle of an activity is based on the callback methods. These callback methods include the UI events as well.

From an instrumented test case, you can use the getInstrumentation() method to get access to an Instrumentation object. This class provides methods related to the system interaction with the application. The complete documentation about this class can be found at: http://developer.android.com/reference/android/app/Instrumentation.html. Some of the most important methods are as follows:

  • The addMonitor method: This method adds a monitor to get information about a particular type of Intent and can be used to look for the creation of an activity. A monitor can be created indicating IntentFilter or displaying the name of the activity to the monitor. Optionally, the monitor can block the activity start to return its canned result. You can use the following call definitions to add a monitor:

    ActivityMonitor addMonitor (IntentFilter filter, ActivityResult result, boolean block).
    ActivityMonitor addMonitor (String cls, ActivityResult result, boolean block).

    The following line is an example line code to add a monitor:

    Instrumentation.ActivityMonitor monitor = getInstrumentation().addMonitor(SecondActivity.class.getName(), null, false);
  • The activity lifecycle methods: The methods to call the activity lifecycle methods are: callActivityOnCreate, callActivityOnDestroy, callActivityOnPause, callActivityOnRestart, callActivityOnResume, callActivityOnStart, finish, and so on. For example, you can pause an activity using the following line code:

  • The getTargetContext method: This method returns the context for the application.

  • The startActivitySync method: This method starts a new activity and waits for it to begin running. The function returns when the new activity has gone through the full initialization after the call to its onCreate method.

  • The waitForIdleSync method: This method waits for the application to be idle synchronously.

The test case methods

JUnit's TestCase class provides the following protected methods that can be overridden by the subclasses:

  • setUp(): This method is used to initialize the fixture state of the test case. It is executed before every test method is run. If you override this method, the first line of code will call the superclass. A standard setUp method should follow the given code definition:

    protected void setUp() throws Exception {
      // Initialize the fixture state
  • tearDown(): This method is used to tear down the fixture state of the test case. You should use this method to release resources. It is executed after running every test method. If you override this method, the last line of the code will call the superclass, shown as follows:

    protected void tearDown() throws Exception {
      // Tear down the fixture state

The fixture state is usually implemented as a group of member variables but it can also consist of database or network connections. If you open or init connections in the setUp method, they should be closed or released in the tearDown method. When testing activities in Android, you have to initialize the activity under test in the setUp method. This can be done with the getActivity() method.

The Assert class and method

JUnit's TestCase class extends the Assert class, which provides a set of assert methods to check for certain conditions. When an assert method fails, AssertionFailedException is thrown. The test runner will handle the multiple assertion exceptions to present the testing results. Optionally, you can specify the error message that will be shown if the assert fails. You can read the Android reference of the TestCase class to examine all the available methods at http://developer.android.com/reference/junit/framework/Assert.html. The assertion methods provided by the Assert superclass are as follows:

  • assertEquals: This method checks whether the two values provided are equal. It receives the actual and expected value that is to be compared with each other. This method is overloaded to support values of different types, such as short, String, char, int, byte, boolean, float, double, long, or Object. For example, the following assertion method throws an exception since both values are not equal:

    assertEquals(true, false);
  • assertTrue or assertFalse: These methods check whether the given Boolean condition is true or false.

  • assertNull or assertNotNull: These methods check whether an object is null or not.

  • assertSame or assertNotSame: These methods check whether two objects refer to the same object or not.

  • fail: This method fails a test. It can be used to make sure that a part of code is never reached, for example, if you want to test that a method throws an exception when it receives a wrong value, as shown in the following code snippet:

      fail("No exception was thrown");
    } catch (NullPointerExceptionn e) {
      // OK

The Android testing API, which extends JUnit, provides additional and more powerful assertion classes: ViewAsserts and MoreAsserts.

The ViewAsserts class

The assertion methods offered by JUnit's Assert class are not enough if you want to test some special Android objects such as the ones related to the UI. The ViewAsserts class implements more sophisticated methods related to the Android views, that is, for the View objects. The whole list with all the assertion methods can be explored in the Android reference about this class at http://developer.android.com/reference/android/test/ViewAsserts.html. Some of them are described as follows:

  • assertBottomAligned or assertLeftAligned or assertRightAligned or assertTopAligned(View first, View second): These methods check that the two specified View objects are bottom, left, right, or top aligned, respectively

  • assertGroupContains or assertGroupNotContains(ViewGroup parent, View child): These methods check whether the specified ViewGroup object contains the specified child View

  • assertHasScreenCoordinates(View origin, View view, int x, int y): This method checks that the specified View object has a particular position on the origin screen

  • assertHorizontalCenterAligned or assertVerticalCenterAligned(View reference View view): These methods check that the specified View object is horizontally or vertically aligned with respect to the reference view

  • assertOffScreenAbove or assertOffScreenBelow(View origin, View view): These methods check that the specified View object is above or below the visible screen

  • assertOnScreen(View origin, View view): This method checks that the specified View object is loaded on the screen even if it is not visible

The MoreAsserts class

The Android API extends some of the basic assertion methods from the Assert class to present some additional methods. Some of the methods included in the MoreAsserts class are:

  • assertContainsRegex(String expectedRegex, String actual): This method checks that the expected regular expression (regex) contains the actual given string

  • assertContentsInAnyOrder(Iterable<?> actual, Object… expected): This method checks that the iterable object contains the given objects and in any order

  • assertContentsInOrder(Iterable<?> actual, Object… expected): This method checks that the iterable object contains the given objects, but in the same order

  • assertEmpty: This method checks if a collection is empty

  • assertEquals: This method extends the assertEquals method from JUnit to cover collections: the Set objects, int arrays, String arrays, Object arrays, and so on

  • assertMatchesRegex(String expectedRegex, String actual): This method checks whether the expected regex matches the given actual string exactly

Opposite methods such as assertNotContainsRegex, assertNotEmpty, assertNotEquals, and assertNotMatchesRegex are included as well. All these methods are overloaded to optionally include a custom error message. The Android reference about the MoreAsserts class can be inspected to learn more about these assert methods at http://developer.android.com/reference/android/test/MoreAsserts.html.

UI testing and TouchUtils

The test code is executed in two different threads as the application under test, although, both the threads run in the same process. When testing the UI of an application, UI objects can be referenced from the test code, but you cannot change their properties or send events. There are two strategies to invoke methods that should run in the UI thread:

  • Activity.runOnUiThread(): This method creates a Runnable object in the UI thread in which you can add the code in the run() method. For example, if you want to request the focus of a UI component:

    public void testComponent() {
        new Runnable() {
          public void run() {
  • @UiThreadTest: This annotation affects the whole method because it is executed on the UI thread. Considering the annotation refers to an entire method, statements that do not interact with the UI are not allowed in it. For example, consider the previous example using this annotation, shown as follows:

    public void testComponent () {

There is also a helper class that provides methods to perform touch interactions on the view of your application: TouchUtils. The touch events are sent to the UI thread safely from the test thread; therefore, the methods of the TouchUtils class should not be invoked in the UI thread. Some of the methods provided by this helper class are as follows:

  • The clickView method: This method simulates a click on the center of a view

  • The drag, dragQuarterScreenDown, dragViewBy, dragViewTo, dragViewToTop methods: These methods simulate a click on an UI element and then drag it accordingly

  • The longClickView method: This method simulates a long press click on the center of a view

  • The scrollToTop or scrollToBottom methods: These methods scroll a ViewGroup to the top or bottom

The mock object classes

The Android testing API provides some classes to create mock system objects. Mock objects are fake objects that simulate the behavior of real objects but are totally controlled by the test. They allow isolation of tests from the rest of the system. Mock objects can, for example, simulate a part of the system that has not been implemented yet, or a part that is not practical to be tested.

In Android, the following mock classes can be found: MockApplication, MockContext, MockContentProvider, MockCursor, MockDialogInterface, MockPackageManager, MockResources, and MockContentResolver. These classes are under the android.test.mock package. The methods of these objects are nonfunctional and throw an exception if they are called. You have to override the methods that you want to use.

Creating an activity test

In this section, we will create an example application so that we can learn how to implement the test cases to evaluate it. Some of the methods presented in the previous section will be put into practice. You can download the example code files from your account at http://www.packtpub.com.

Our example is a simple alarm application that consists of two activities: MainActivity and SecondActivity. The MainActivity implements a self-built digital clock using text views and buttons. The purpose of creating a self-built digital clock is to have more code and elements to use in our tests. The layout of MainActivity is a relative one that includes two text views: one for the hour (the tvHour ID) and one for the minutes (the tvMinute ID). There are two buttons below the clock: one to subtract 10 minutes from the clock (the bMinus ID) and one to add 10 minutes to the clock (the bPlus ID). There is also an edit text field to specify the alarm name. Finally, there is a button to launch the second activity (the bValidate ID). Each button has a pertinent method that receives the click event when the button is pressed. The layout looks like the following screenshot:

The SecondActivity receives the hour from the MainActivity and shows its value in a text view simulating that the alarm was saved. The objective to create this second activity is to be able to test the launch of another activity in our test case.


In this article, you learned how to use unit tests that allow developers to quickly verify the state and behavior of an activity on its own.

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