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This tutorial describes how to write unit and instrumentation tests for your Android application. It describes how to execute these tests via Android studio and Gradle. This tutorial assumes that you are familiar with Android programming in general.

1. Introduction into Android testing

1.1. Testing Android applications

Android applications run on devices with limited memory, CPU power and power supply. The behavior of the application also depends on external factors like connectivity, general system utilization, etc. Therefore, it is very important to debug, test and optimize your Android application. Having a reasonable test coverage for your Android application helps you to enhance and maintain the Android application.

As it is not possible to test Android applications on all possible device configurations, it is a common practice to run Android tests on typical device configurations. You should test your application at least on one device with the lowest possible configuration. In addition you should test on one device with the highest available configuration, e.g., pixel density, screen resolution to ensure that it works fine on these devices.

Unit testing for Android can be classified into:

  • Local unit tests - tests which can run on the JVM. If possible, you should prefer to use local tests. Local tests run much faster compared to the time required to deploy and run the test on an Android device.

  • Instrumented unit tests - tests which require the Android system. If you want to test code which use the Android API, you need to run these tests on an Android device. Unfortunately, this makes the execution time of the tests longer.

Android testing categories

1.2. What to test on Android applications

You should focus your Android tests on testing the business logic of your application. A good rule of thumb is to have the following distribution of tests:

  • 70-80 % unit tests to ensure stability of your code basis

  • 20-30 % functional tests to ensure that the application really works

  • some cross functional tests if your application integrates intensively with other Application components

Testing Strategy for Android

Another important criteria for testing is if you only test your own application or if you test the integration with other applications. If you run tests within your application, you can use testing frameworks which require some knowledge about your application, e.g., the view IDs.

1.3. Testing preconditions

It is good practice in Android testing to have one method called testPreconditions() which tests the pre-conditions for all other tests. If this method fails, you know immediately that the assumptions for the other tests have been violated.

1.4. Tooling support for Android testing

The Android Testing Support library (ATSL) support testing with a JUnit 4-compatible test runner (AndroidJUnitRunner). You can run unit tests either on the Java virtual machine or on an Android runtime. Also, Google provides a user interface testing framework called Espresso which allows developing Android user interface tests.

To allow running Android unit tests on the JVM, the Android Gradle plug-in creates a special version of the android.jar (also known as the Android mockable jar). This file is provided to the unit test so that all fields, methods and classes are available. Any call to the Android mockable JAR results, by default, in an exception.

Therefore, if your classes do not call the Android API, you can use the JUnit test framework (or any other Java testing framework) without any restrictions. If you have dependencies to the Android API, these dependencies in your code must be replaced for the unit tests, e.g., via a mocking framework like Mockito. See Activating default return values for mocked methods in android.jar for information how to define that default values should be returned from the Android mockable jar.

The Android Testing Support Library provides functionality to create and run Android tests. The library contains the AndroidJUnitRunner, the Espresso test framework and the UI Automator.

AndroidJUnitRunner allows to create and run JUnit 4 tests, while the Espresso test framework can be used to test the User Interface of your application. UI Automator allows to write cross application functional tests.

AndroidJunitRunner provides access to the instrumentation API, via the InstrumentationRegistery.

  • InstrumentationRegistry.getInstrumentation(), returns the Instrumentation currently running.

  • InstrumentationRegistry.getContext(), returns the Context of this Instrumentation’s package.

  • InstrumentationRegistry.getTargetContext(), returns the application Context of the target application.

  • InstrumentationRegistry.getArguments(), returns a copy of arguments Bundle that was passed to this Instrumentation. This is useful when you want to access the command line arguments passed to Instrumentation for your test.

It also gives access to the life cycle via the ActivityLifecycleMonitorRegistry.

2. Android project structure and test folder creation

2.1. Android project organization for tests

The preferred way of organizing Android tests is based on a convention. In your application project, you should use the following base folder structure for your code organization. This is also the structure the Android project wizard creates.

  • app/src/main/java- for your source code of your main application build

  • app/src/test/java - for any unit test which can run on the JVM

  • app/src/androidTest/java - for any test which should run on an Android device

If you follow this conversion, then the Android build system can automatically run your tests on the correct target (JVM or Android device).

2.2. Solving the "error duplicate files in path" error

If you receive the following error message: "error duplicate files in path. Path in archive: LICENSE.txt" you can add the following to your app/gradle.build file.

android {
    packagingOptions {
    exclude 'LICENSE.txt'

3. Unit testing on the JVM

3.1. Unit testing in Android

Android uses the term unit tests for tests which can run on a local JVM or the Android Runtime.

A unit test verifies in isolation the functionality of a certain component. For example, assume a button in an Android activity is used to start another activity. A unit test would determine, if the corresponding intent was issued, not if the second activity was started

The unit tests are executed against a modified version of the android.jar Android library where all final modifiers have been stripped off. This allow you to use mocking libraries, like Mockito.

3.2. Location of unit tests

As described in Android project organization for tests the unit tests of an Android project should be located in the app/src/test folder. See Test folder creation in Android Studio for the creation of such a test folder.

3.3. Required dependencies in the Gradle build file

To use JUnit tests for your Android application, you need to add the it as dependency to your Gradle build file.

dependencies {
    // Unit testing dependencies
    testCompile 'junit:junit:4.12'
    // Set this dependency if you want to use the Hamcrest matcher library
    testCompile 'org.hamcrest:hamcrest-library:1.3'
    // more stuff, e.g., Mockito

3.4. Run the unit tests from Gradle

Run your unit tests with the gradlew test command.

3.5. Run the unit tests from Android Studio

To run a unit test, right-click on your test class in the Project window and select Run.

Running Unit tests in Android Studio

3.6. Location of test reports

The Test reports are created in the app/build/reports/tests/debug/`directory. The `index.html gives an overview and links to the individual test pages.

3.7. Activating default return values for mocked methods in android.jar

By default, all calls to methods in the modified android.jar file throw exceptions. This default should ensure that your unit tests only test your code and do not depend on any particular behavior of the Android platform. If you want to configure a certain behavior, you can use a mocking framework to replace these call.

You can also instruct the Gradle build system to return default values for method calls in the `android.jar`with the following configuration in your Gradle build file.

android {
  // ...
  testOptions {
    unitTests.returnDefaultValues = true

4. Exercise: Write an Android unit test

4.1. Preparation: Create Android project

Create the Android project as described in Android temperature converter.

4.2. Exercise: Create unit test

4.2.1. Target of this exercise

In this exercise you learn how to create a simple JUnit4 test for an Android project.

4.2.2. Add JUnit dependency

Ensure you have the dependency to Junit in your app/build.gradle file. If the test folder is missing in your project, follow the process described in Test folder creation in Android Studio to create it.

dependencies {
        // Unit testing dependencies
        testCompile 'junit:junit:4.12'

4.2.3. Create test

In your app/src/test directory create the following two test methods for the ConverterUtil class.

package com.vogella.android.temperature.test;

import static org.junit.Assert.*;

import org.junit.After;
import org.junit.Before;
import org.junit.Test;

import com.vogella.android.temperature.ConverterUtil;

public class ConverterUtilTest {

        public void testConvertFahrenheitToCelsius() {
                float actual = ConverterUtil.convertCelsiusToFahrenheit(100);
                // expected value is 212
                float expected = 212;
                // use this method because float is not precise
                assertEquals("Conversion from celsius to fahrenheit failed", expected,
                                actual, 0.001);

        public void testConvertCelsiusToFahrenheit() {
                float actual = ConverterUtil.convertFahrenheitToCelsius(212);
                // expected value is 100
                float expected = 100;
                // use this method because float is not precise
                assertEquals("Conversion from celsius to fahrenheit failed", expected,
                                actual, 0.001);


4.2.4. Run unit tests

Ensure your unit tests are correctly implemented by running test tests. They should run successfully.

5. Writing Instrumentation tests to run on the Android device

5.1. Instrumentation tests

The Android testing API provides hooks into the Android component and application life cycle. These hooks are called the instrumentation API and allow your tests to control the life cycle and user interaction events.

Under normal circumstances your application cannot control the life cycle events and the user drives the application. For example, if Android creates your activity the onCreate() method is called. Or if the user presses a button your corresponding code is called. Via instrumentation you can control these events via your test code. For example, your instrumentation test can start the activity. Afterwards, it can call the finish() and restart the activity to test if the instance state of the activity is correctly restored.

Instrumented unit tests are unit tests that run on Android devices and emulators instead of running on the Java virtual machine. These tests have access to the real device and its resources and are useful to unit test functionality which cannot be easily mocked by mocking frameworks. An example is a test which validates a Parcelable implementation.

An instrumentation-based test class allows you to send key events (or touch events) to the application under test.

With user interface testing framework like Espresso, the developer rarely has to use the instrumentation API directly.

5.2. How the Android system executes tests

The InstrumentationTestRunner is the base test runner for Android tests. This test runner starts and loads the test methods. Via the instrumentation API it communicates with the Android system. If you start a test for an Android application, the Android system kills any process of the application under test and then loads a new instance. It does not start the application, this is the responsibility of the test methods. The test method controls the life cycle of the components of the application.

The test runner also calls the onCreate() method of the application and activity under test during its initialization.

5.3. Mocking objects in Android

The mocking framework Mockito can also be used for instrumentation tests. This allows you to replace parts of the Android system which are not interesting for the test. The Android framework provided in the past specialized mocking classes but these are not necessary anymore.

5.4. Location of instrumentation tests

As described in Android project organization for tests the unit tests of an Android project should be located in the app/src/androidTest/java folder. See Test folder creation in Android Studio for the creation of such a test folder.

5.5. Define dependencies and testInstrumentationRunner in the Gradle build file

To use JUnit tests for your Android application you need to add the dependency to JUnit to your Gradle build file. You also need to specify android.support.test.runner.AndroidJUnitRunner as testInstrumentationRunner in the build file.

defaultConfig {
       ..... more stuff
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"

dependencies {
    // Unit testing dependencies
    androidTestCompile 'junit:junit:4.12'
    // Set this dependency if you want to use the Hamcrest matcher library
    androidTestCompile 'org.hamcrest:hamcrest-library:1.3'
    // more stuff, e.g., Mockito

5.6. Using the @RunWith(AndroidJUnit4.class)

It is also recommended annotating the test with the @RunWith(AndroidJUnit4.class) annotation. AndroidJUnit4 extends JUnit4, so if you use pure Junit4 syntax and ActivityTestRule it is not required. But you need it, if you want to run, i.e., Espresso tests with ActivityTestRule and JUnit4.

5.7. Run the unit tests from Gradle

Run your unit tests with the gradlew connectedCheck command.

5.8. Run the unit tests from Android Studio

Right-click on your test class in the Project window and select Run.

5.9. Location of test reports

The test reports are created in the app/build/reports/androidTests/connected/ directory. The index.html gives an overview and links to the individual test pages.

5.10. How to replace the application for instrumentation tests

You can replace the application class for the instrumentation tests by overriding the AndroidJUnitRunner and its newApplication method.

package com.vogella.android.daggerjunitmockito;

import android.app.Application;

public class MyMockApplication extends Application {

    public void onCreate() {
       // do something important for your tests here

Test runner

package com.vogella.android.daggerjunitmockito;

import android.app.Application;
import android.content.Context;
import android.support.test.runner.AndroidJUnitRunner;

public class MockTestRunner extends AndroidJUnitRunner {
  public Application newApplication(ClassLoader cl, String className, Context context)
      throws InstantiationException, IllegalAccessException, ClassNotFoundException {
    return super.newApplication(cl, MyMockApplication.class.getName(), context);

And you need to register this test runner in your build.gradle file.

android {
    /// more
        testInstrumentationRunner "com.vogella.android.daggerjunitmockito.MockTestRunner"
    /// more

6. Exercise: Mocking file access

6.1. Target of this exercise

It is not required to use this class in your Android application. It is only used to demonstrate the usage of Mockito in a unit test.

6.2. Create class to test

In an existing or in a new Android application with the package com.vogella.android.testing.mockitocontextmock add the following class.

public class Util {
        public static void writeConfiguration(Context ctx ) {
                try (FileOutputStream openFileOutput =
                         ctx.openFileOutput( "config.txt", Context.MODE_PRIVATE);) {

                        openFileOutput.write("This is a test1.".getBytes());
                        openFileOutput.write("This is a test2.".getBytes());
                } catch (Exception e) {
                        // not handled

6.3. Create a new unit test

Using Mockito the mocking framework, write a unit test which validates that: * openFileOutput is called exactly once * the write() method is called at least twice.

package com.vogella.android.testing.mockitocontextmock;

import android.content.Context;

import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.mockito.Mock;
import org.mockito.MockitoAnnotations;

import java.io.FileOutputStream;

import static org.junit.Assert.fail;
import static org.mockito.Matchers.any;
import static org.mockito.Matchers.anyInt;
import static org.mockito.Matchers.anyString;
import static org.mockito.Mockito.atLeast;
import static org.mockito.Mockito.times;
import static org.mockito.Mockito.verify;
import static org.mockito.Mockito.when;

public class TextContextOutputStream {

Context context;

FileOutputStream fileOutputStream;

public void init(){

public void writeShouldWriteTwiceToFileSystem() {
    try {
        when(context.openFileOutput(anyString(), anyInt())).thenReturn(fileOutputStream);
        verify(context, times(1)).openFileOutput(anyString(), anyInt());
        verify(fileOutputStream, atLeast(2)).write(any(byte[].class));

    } catch (Exception e) {

7. Activity testing

8. More on Android testing

8.1. Android additional assertion

The Android testing API provides the MoreAsserts and ViewAsserts classes in addition to the standard JUnit Assert class.

8.2. Test groups

The @SmallTest, `@MediumTest`and `@LargeTest`annotations allows to classify tests.

This allows you to run, for example, only short running tests. You may run your long running tests on a continuous integration server.

To run only selected tests you can configure the InstrumentationTestRunner via your Gradle plug-in. The following listing is an example for your build.gradle file to run only the tests annotated with @SmallTests.

android {
  defaultConfig {
    testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    testInstrumentationRunnerArgument "size", "small"
import android.test.suitebuilder.annotation.MediumTest;
import android.test.suitebuilder.annotation.SmallTest;

import org.junit.Test;

public class ExampleTest {

    public void validateSecondActivity() {
        // Do something not so long...

    public void validateSecondActivityAgain() {
        // Do something which takes more time....


8.3. Test filtering

You can annotate tests with annotations. The Android test runner allows to filter these tests.

Table 1. Annotations for filtering tests
Annotation Description


Specifies that the test should run only on physical devices, not on emulators.



8.4. Flaky tests

Actions in Android are sometimes time dependent. To tell Android to repeat a test once it fails, use the @FlakyTest annotation. Via the tolerance attribute of this annotation you can define how many times the test should be repeated before marking it as failed.

9. Exercise: Life cycle test

9.1. Target of this exercise

In this exercise the instrumentation test framework is demonstrated. For such test you would typically use higher level frameworks, like Espresso.

9.2. Create project which is tested

Create a new Android project called com.vogella.android.test.simpleactivity with the activity called MainActivity.

Add a second activity called SecondActivity to your project. This activity should use a layout with at least one TextView. The id of the TextView should be "resultText" and its text should be set to "Started".

Add an EditText field to the layout of the MainActivity class.

Add a button to the layout used by your MainActivity activity. If this button is clicked, the second activity should be started.

Put the text EditText field as extra into the intent using "text" as key. Also put the "http://www.vogella.com" String as extra into the intent and use the key "URL" for this.

Here is some example code for the MainActivity.

package testing.android.vogella.com.simpleactivity;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;

public class MainActivity extends Activity {

    protected void onCreate(Bundle savedInstanceState) {

    public void onClick(View view) {
        Intent intent = new Intent(this, SecondActivity.class);
        intent.putExtra("URL", "http://www.vogella.com");

9.3. Create test project and class

Create a new instrumentation test similar to the following.

package com.vogella.android.test.simpleactivity.test;

import android.app.Activity;
import android.app.Instrumentation;
import android.app.Instrumentation.ActivityMonitor;
import android.test.ActivityInstrumentationTestCase2;
import android.test.TouchUtils;
import android.test.UiThreadTest;
import android.test.ViewAsserts;
import android.view.KeyEvent;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

import com.vogella.android.test.simpleactivity.R;

import com.vogella.android.test.simpleactivity.MainActivity;
import com.vogella.android.test.simpleactivity.SecondActivity;

public class SecondActivityFunctionalTest extends
                ActivityInstrumentationTestCase2<SecondActivity> {

        private static final String NEW_TEXT = "new text";

        public SecondActivityFunctionalTest() {

        public void testSetText() throws Exception {

                SecondActivity activity = getActivity();

                // search for the textView
                final TextView textView = (TextView) activity

                // set text
                getActivity().runOnUiThread(new Runnable() {

                        public void run() {

                assertEquals("Text incorrect", NEW_TEXT, textView.getText().toString());


        public void testSetTextWithAnnotation() throws Exception {

                SecondActivity activity = getActivity();

                // search for the textView
                final TextView textView = (TextView) activity

                assertEquals("Text incorrect", NEW_TEXT, textView.getText().toString());



10. Using the Monkey tool for creating a random event stream

10.1. What is monkey?

Monkey is a command line tool which sends pseudo random events to your device. You can restrict Monkey to run only for a certain package and therefore instruct Monkey to test only your application.

10.2. How to use Monkey

The following command sends 2000 random events to the application with the de.vogella.android.test.target package.

adb shell monkey -p de.vogella.android.test.target -v 2000

Monkey sometimes causes problems with the adb server. Use the following commands to restart the adb server.

adb kill-server
adb start-server

You can use the -s [seed] parameter to ensure that the generated sequence of events is always the same.

For more info on Monkey please see the Monkey description.

11. Application testing

The application class contains the logic, data and settings which are relevant for the whole application. Therefore you should test this object, to ensure it works correctly.

You can write a JUnit 4 test for the application object and test it on the JVM. In this case you would mock all dependencies to the application object. To test an Android application object on the Android runtime you use the ApplicationTestCase class. It is expected that Google will soon provide a special JUnit4 rule for testing the application object but at the moment this is not yet available.

The test runner of the Android tests (InstrumentationTestRunner) creates automatically an instance of application during its initialization phase. If you do asynchronous processing in your onCreate method you should consider that.

12. Exercise: Testing the Android application

12.1. Create project

Create a new Android application with the com.vogella.android.testing.applicationtest package name based on the Empty Activity template.

Add the following application object to your application.

package com.vogella.android.testing.applicationtest;

import android.app.Application;

import java.util.ArrayList;
import java.util.List;

public class MyApplication extends Application {
    public static final List<String> list = new ArrayList<String>();

Also declare the application it in your manifest file.

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.vogella.android.testing.applicationtest" >

        android:theme="@style/AppTheme" >
            android:label="@string/app_name" >
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />


12.2. Create unit test for application object

In your app/src/test directory create a new unit test. Assert that the MyApplication.list field is not empty and has initially a size of zero.

12.3. Create instrumented test for application object

Create the following unit test based on the JUnit 3 testing framework.

package com.vogella.android.testing.applicationtest;

import android.content.pm.PackageInfo;
import android.test.ApplicationTestCase;
import android.test.MoreAsserts;

public class ApplicationTest extends ApplicationTestCase<MyApplication> {

    private MyApplication application;

    public ApplicationTest() {

    protected void setUp() throws Exception {
        application = getApplication();


    public void testCorrectVersion() throws Exception {
        PackageInfo info = application.getPackageManager().getPackageInfo(application.getPackageName(), 0);
        MoreAsserts.assertMatchesRegex("\\d\\.\\d", info.versionName);


13. Testing other components

13.1. Service testing

To test a service you use the ServiceTestRule class from the Android Testing Support Library. The old ServiceTestCase is deprecated.

This rule provides a simplified mechanism to start and shutdown your service before and after your test. It guarantees that the service is successfully connected when starting (or binding to) a service. The service can be started (or bound) using one of the helper methods. It will automatically be stopped (or unbound) after the test completes and any methods annotated with @After are finished.

This rule doesn’t support IntentService because it’s automatically destroyed after the onHandleIntent method.

The following listing is an example of testing a service.

public class MyServiceTest {

    public final ServiceTestRule mServiceRule = new ServiceTestRule();

    // test for a service which is started with startService
    public void testWithStartedService() {
        startService(new Intent(InstrumentationRegistry.getTargetContext(),
        // test code

 // test for a service which is started with bindService
    public void testWithBoundService() {
        IBinder binder = mServiceRule.
                        bindService(new Intent(InstrumentationRegistry.getTargetContext(),
        MyService service = ((MyService.LocalBinder) binder).getService();
        assertTrue("True wasn't returned", service.doSomethingToReturnTrue());
adb kill-server
adb start-server

13.2. Content provider testing

To test a content provider, you use the ProviderTestCase2 class. ProviderTestCase2 automatically instantiates the provider under test and inserts an IsolatedContext object. This context is isolated from the Android system, but still allows file and database access. The usage of the IsolatedContext object ensures that your provider test does not affect the real device.

ProviderTestCase2 also provides access to a MockContentResolver via the getMockContentResolver() method.

You should test all operations of the provider and also what happens if the provider is called with an invalid URI or with an invalid projection.

13.3. Loader testing

To test a loader, you use the `LoaderTestCase`class. It is expected that a JUnit 4 rule will be provided in the future to replace this class.

14. Support annotations

Google provides a new annotations package. This package includes a number of metadata annotations, which you can use in your code, to prevent bugs.

To use these annotations add the following dependency to your Gradle build file.

dependencies {
    compile 'com.android.support:support-annotations:22.2.0'

The following information describes the most important annotations. See http://tools.android.com/tech-docs/support-annotations for more information.

14.1. Nullness Annotations

The @Nullable annotation can be used to indicate that a given parameter or return value can be null. Similarly, the @NonNull annotation can be used to indicate that a given parameter (or return value) can not be null.

14.2. Threading Annotations: @UiThread, @WorkerThread, …​

If a method can only be called from a specific type of thread, you can annotate it with one of the following annotations:

  • @UiThread

  • @MainThread

  • @WorkerThread

  • @BinderThread


protected abstract Result doInBackground(Params... params);

  protected void onProgressUpdate(Progress... values) {

15. Creating code coverage report

A code coverage report shows you how much of your application code is covered by tests. To create such a report, you can create a separate launch configuration. For this, select your package and select menu:[Create Tests in…​].

android code coverage10

You can now create a runtime configuration for the code coverage. If you run it a report is generated.

android code coverage20
android code coverage30
android code coverage40

16. Test folder creation in Android Studio

The recent versions of Android Studio has added a test folder to its default project template. In case you are using a template which does not create a test folder, you have to create it manually. To create the test folder in Android Studio, switch to the Project view, this shows you the directory structure of your project.

Switching to the Project view in Android Studio

Select the src and use the context menu to create a new test folder.

Switching to the Project view in Android Studio
Adding a java folder
Adding a java folder

If not yet done, also add the JUnit dependency to your Gradle build file.

dependencies {
    // Unit testing dependencies
    testCompile 'junit:junit:4.12'
    // Set this dependency if you want to use the Hamcrest matcher library
    testCompile 'org.hamcrest:hamcrest-library:1.3'
    // more stuff, e.g., Mockito

The creation of the Java folder might add the new test directory as source file to your build.gradle file. If you have the following entry in your app/build.gradle file you need to REMOVE it. test should NOT be treated as normal source folder.

 sourceSets { main { java.srcDirs = ['src/main/java', 'src/test/java/'] } }

Afterwards you can add your unit test to this folder structure.

17. About this website

18. Android testing resources

18.1. vogella GmbH training and consulting support


The vogella company provides comprehensive training and education services from experts in the areas of Eclipse RCP, Android, Git, Java, Gradle and Spring. We offer both public and inhouse training. Whichever course you decide to take, you are guaranteed to experience what many before you refer to as “The best IT class I have ever attended”.

The vogella company offers expert consulting services, development support and coaching. Our customers range from Fortune 100 corporations to individual developers.

Copyright © 2012-2016 vogella GmbH. Free use of the software examples is granted under the terms of the EPL License. This tutorial is published under the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Germany license.

See Licence.