Getting Started with Testing —

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.

// Android的测试基于JUnit

Test Types

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:

//对于每一个项目的模块，Androidstudio都会包含这两个类型的source sets

Local unit tests

Located at module-name/src/test/java/.

These tests run on the local JVM and do not have access to functional Android framework APIs.

// 这些测试运行在本地JAVA虚拟机上，不会访问Android框架层的api

To get started, see Building Local Unit Tests.

Instrumented tests

Located at module-name/src/androidTest/java/.

These are all tests that must run on an Android hardware device or an Android emulator.

//这些测试必须运行在Android硬件设备上或者模拟器上

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.

//instruments test构建了一个apk和你的app一起安装，系统会让你的app和测试apk一同运行在同一个进程，这样你的测试可以调用应用中的方法并且可以修改变量，让和应用的交互变得自动化

For information about how to create instrumented tests, see the following topics:

Building Instrumented Unit Tests: Build complex unit tests with Android dependencies that cannot be satisfied with mock objects.
Automating User Interface Tests: Create tests to verify that the user interface behaves correctly for user interactions within a single app or for interactions across multiple apps.
Testing App Component Integrations: Verify the behavior of components that users do not directly interact with, such as a Service or aContent Provider.

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.

//然而上面描述的local unit test and instrumentes test只是帮助区分他们一个是运行在本地虚拟机，一个是运行在Android平台上。真正的测试类型的分类应该是如下表描述的：

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 Espressoallow 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.

Test APIs

The following are common APIs used for testing apps on Android.

JUnit

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:

//你可以通过下面的注解唤起一些代码段用户特殊的处理

@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. // 用before注解来指定包含test代码构建操作的代码块。测试类调用这个代码块在所有测试代码之前，你可以有多个before声明的代码块，但是他们的相对运行顺序是没法保证的
@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 // after注解指定了包含有测试类的拆除工作的代码块。测试类调用这个代码在所有测试方法之后，你可以定义多个after注解代码块。使用这个注解来释放内存中的资源
@Test: Use this annotation to mark a test method. A single test class can contain multiple test methods, each prefixed with this annotation. //使用test注解来标记测试方法，一个测试类可以包含多个测试方法，每一个方法都带有test前缀
@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. //rule允许你灵活添加和冲定义每一个测试方法的行为以便重用。在Android 测试中，会以它和其他的测试规则类一起使用，例如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. //使用这个注解来指定一个对于每一个测试类只会调用一次的静态方法，这个测试搭建方法对于开销较大的操作例如连接数据库等是非常有帮助的。
@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). //一些注释支持添加可以设置值的元素的功能，例如你可以指定一个超市时间对于这个测试。如果测试开始但是没有在超时时间内完成，他会自动失败，超时时间以毫秒指定

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.

Android Testing Support Library

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:

AndroidJUnitRunnerA JUnit 4-compatible test runner for Android.EspressoA UI testing framework; suitable for functional UI testing within an app.UI AutomatorA UI testing framework suitable for cross-app functional UI testing between both system and installed apps.

Assertion classes

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.

Monkey and monkeyrunner

The Android SDK includes two tools for functional-level app testing:

Monkey: This is a command-line tool that sends pseudo-random streams of keystrokes, touches, and gestures to a device. You run it with the Android Debug Bridge (adb) tool, and use it to stress-test your app, report back errors any that are encountered, or repeat a stream of events by running the tool multiple times with the same random number seed.
monkeyrunner: This tool is an API and execution environment for test programs written in Python. The API includes functions for connecting to a device, installing and uninstalling packages, taking screenshots, comparing two images, and running a test package against an app. Using the API, you can write a wide range of large, powerful, and complex tests. You run programs that use the API with the monkeyrunner command-line tool.

Guides for Building Android Tests

The following documents provide more detail about how to build and run a variety of test types:

Building Local Unit Tests: Build unit tests that have no dependencies or only simple dependencies that you can mock, which run on your local JVM.
Building Instrumented Unit Tests: Build complex unit tests with Android dependencies that cannot be satisfied with mock objects, which run on a hardware device or emulator.
Automating User Interface Tests: Create tests to verify that the user interface behaves correctly for user interactions within a single app or for interactions across multiple apps.
Testing App Compontent Integrations: Verify the behavior of components that users do not directly interact with, such as a service or a content provider.
Testing Display Performance: Write tests that measure your app's UI performance to ensure a consistently smooth user experience.