Android tests are based on JUnit, and you can run them either as local unit tests on the JVM or as instrumented tests on an Android device. This page provides an introduction to the concepts and tools for building Android tests.
When using Android Studio to write any of your tests, your test code must go into one of two different code directories (source sets). For each module in your project, Android Studio includes both source sets, corresponding to the following test types:
module-name/src/test/java/.
These tests run on the local JVM and do not have access to functional Android framework APIs.
To get started, see Building Local Unit Tests.
module-name/src/androidTest/java/.
These are all tests that must run on an Android hardware device or an Android emulator.
Instrumented tests are built into an APK that runs on the device alongside your app under test. The system runs your test APK and your app under tests in the same process, so your tests can invoke methods and modify fields in the app, and automate user interaction with your app.
For information about how to create instrumented tests, see the following topics:
However, the local unit tests and instrumented tests described above are just terms that help distinguish the tests that run on your local JVM from the tests that run on the Android platform (on a hardware device or emulator). The real testing types that you should understand when building a complete test suite are described in the following table.
| Type | Subtype | Description |
|---|---|---|
| Unit tests | ||
| Local Unit Tests | Unit tests that run locally on the Java Virtual Machine (JVM). Use these tests to minimize execution time when your tests have no Android framework dependencies or when you can mock the Android framework dependencies. | |
| Instrumented unit tests |
Unit tests that run on an Android device or emulator. These tests have
access to Instrumentation
information, such as the Context of the app you are
testing. Use these tests when your tests have Android dependencies that mock
objects cannot satisfy.
|
|
| Integration Tests | ||
| Components within your app only | This type of test verifies that the target app behaves as expected when a user performs a specific action or enters a specific input in its activities. For example, it allows you to check that the target app returns the correct UI output in response to user interactions in the app’s activities. UI testing frameworks like Espresso allow you to programmatically simulate user actions and test complex intra-app user interactions. | |
| Cross-app Components | This type of test verifies the correct behavior of interactions between different user apps or between user apps and system apps. For example, you might want to test that your app behaves correctly when the user performs an action in the Android Settings menu. UI testing frameworks that support cross-app interactions, such as UI Automator, allow you to create tests for such scenarios. |
The following are common APIs used for testing apps on Android.
You should write your unit or integration test class as a JUnit 4 test class. The framework offers a convenient way to perform common setup, teardown, and assertion operations in your test.
A basic JUnit 4 test class is a Java class that contains one or more test
methods. A test method begins with the @Test annotation and
contains the code to exercise and verify a single functionality (that is, a
logical unit) in the component that you want to test.
The following snippet shows an example JUnit 4 integration test that uses the Espresso APIs to perform a click action on a UI element, then checks to see if an expected string is displayed.
@RunWith(AndroidJUnit4.class)
@LargeTest
public class MainActivityInstrumentationTest {
@Rule
public ActivityTestRule mActivityRule = new ActivityTestRule<>(
MainActivity.class);
@Test
public void sayHello(){
onView(withText("Say hello!")).perform(click());
onView(withId(R.id.textView)).check(matches(withText("Hello, World!")));
}
}
In your JUnit 4 test class, you can call out sections in your test code for special processing by using the following annotations:
@Before: Use this annotation to specify a block of code that
contains test setup operations. The test class invokes this code block before
each test. You can have multiple @Before methods but the order in
which the test class calls these methods is not guaranteed.@After: This annotation specifies a block of code that
contains test tear-down operations. The test class calls this code block after
every test method. You can define multiple @After operations in
your test code. Use this annotation to release any resources from memory.@Test: Use this annotation to mark a test method. A single
test class can contain multiple test methods, each prefixed with this
annotation.@Rule: Rules allow you to flexibly add or redefine the
behavior of each test method in a reusable way. In Android testing, use this
annotation together with one of the test rule classes that the Android Testing
Support Library provides, such as ActivityTestRule
or ServiceTestRule.@BeforeClass: Use this annotation to specify static methods
for each test class to invoke only once. This testing step is useful for
expensive operations such as connecting to a database.@AfterClass: Use this annotation to specify static methods for
the test class to invoke only after all tests in the class have run. This
testing step is useful for releasing any resources allocated in the
@BeforeClass block.@Test(timeout=): Some annotations support the ability to pass
in elements for which you can set values. For example, you can specify a
timeout period for the test. If the test starts but does not complete within
the given timeout period, it automatically fails. You must specify the timeout
period in milliseconds, for example: @Test(timeout=5000).For more annotations, see the documentation for JUnit annotations and the Android annotations.
Use the JUnit Assert class to verify the
correctness of an object's state. The assert methods compare values you expect
from a test to the actual results and throw an exception if the comparison
fails. Assertion classes describes these
methods in more detail.
The Android Testing Support Library provides a set of APIs that allow you to quickly build and run test code for your apps, including JUnit 4 and functional UI tests. The library includes the following instrumentation-based APIs that are useful when you want to automate your tests:
Because Android Testing Support Library APIs extend JUnit, you can use assertion methods to display the results of tests. An assertion method compares an actual value returned by a test to an expected value, and throws an AssertionException if the comparison test fails. Using assertions is more convenient than logging, and provides better test performance.
To simplify test development, you should use the Hamcrest library, which lets you create more flexible tests using the Hamcrest matcher APIs.
The Android SDK includes two tools for functional-level app testing:
monkeyrunner command-line tool.The following documents provide more detail about how to build and run a variety of test types: