本文为一旬一题写作计划中单元测试专题内文章，读完本篇大约需要5分钟。

技术点

Service 涉及的 Android 类很多，所以要用设备测试（Instrumentation Test），也就是测试代码要放在 module-name/src/androidTest/java/。本文的测试方案会用到 RestrictTo + Junit4 + AndroidJUnitRunner。下面做个简单介绍：

RestrictTo注解

android.support.annotation 包下定义的一个注解: > Denotes that the annotated element should only be accessed from within a specific scope (as defined by RestrictTo.Scope).

用来表示被注解的元素只能在限定范围内（library，tests，子类）被访问。比如只在测试中有效的方法，可以这样写。

@RestrictScope(TESTS)
public abstract int getUserId();

遗憾的是，目前这个注解只起到提示作用，即便不在限定范围内访问，也不会发生什么。不过即将到来的AndroidStudio 2.3 版本中这方面会加强，在Lint的时候会提出警告。期待期待～

AndroidJUnitRunner

设备测试本身不支持JUnit4。AndroidJUnitRunner 类是一个 JUnit 测试运行器，可让您在 Android 设备上运行 JUnit 3 或 JUnit 4 样式测试类。

添加依赖

dependencies {
            compile 'com.android.support:support-annotations:22.2.0'
            androidTestCompile 'com.android.support.test:runner:0.4.1'
            }

指定 testInstrumentationRunner:

 android {
            defaultConfig {
                testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
            }
            }

给测试类加上注解 :
```
@RunWith(AndroidJUnit4.class)
        
```
然后就可以写Junit4测试代码了。

实战

比如项目中的一个模块（比如下面的 TheSDK ），初始化完成的时候，应该要启动了某个Service。这个逻辑要怎么测试？

public class TheSDK {
    private static void init(@NonNull final Context context) {
        // .....
        startServices(context);
        
        // .....
    }
    private static void startServices(final @NonNull Context context) {
        context.startService(new Intent(context, Service1.class));
    }
    public static class Builder {
        // .....
        public void init() {
            TheSDK.init(...);
        }
    }
    }

首先用RestrictTo对Service1做一点改造，具体看注释：

public class Service1 extends Service {
    @RestrictTo (RestrictTo.Scope.TESTS)
    static boolean started;//增加一个只在测试中用的标志位
    private SomeBroadCastReceiver receiver;
    public Service1() {
    }
    @Override
    public IBinder onBind(Intent intent) {
        throw null;
    }
    @Override
    public int onStartCommand(final Intent intent, final int flags, final int startId) {
        return START_STICKY;
    }
    @Override
    public void onCreate() {
        super.onCreate();
        started = true;//标记启动完成
        //...init broadcast receiver and whatnot
    }
    @Override
    public void onDestroy() {
        unregisterReceiver(receiver);
        super.onDestroy();
    }
    }

然后给测试类加上注解，指定运行器为 AndroidJUnit4，写测试断言，搞定！：

@RunWith (AndroidJUnit4.class) // <<----Make sure you add this!!!!
public class TheSDKTest {
    @Test
    public void test_services_started_on_init() throws TimeoutException {
        final Context context = InstrumentationRegistry.getTargetContext();
        new TheSDK.Builder(context).init();
        assertTrue(Service1.started);
    }
    }

（Tips: Service的测试改造代码可以封装在BaseService中，就不用重复手写了）

class BaseService extends Service {
    @RestrictTo (RestrictTo.Scope.TESTS)
    private static boolean isServiceStarted;
    @Override
    public IBinder onBind(Intent intent) {
        throw null;
    }
    @Override
    public int onStartCommand(final Intent intent, final int flags, final int startId) {
        return START_STICKY;
    }
    @Override
    public void onCreate() {
        super.onCreate();
        isServiceStarted = true;
    }
    @Override
    public void onDestroy() {
        super.onDestroy();
        isServiceStarted = false;
    }
    public static boolean isServiceStarted() {
        return isServiceStarted;
    }
    }
/**
而且Service可以拎出来单独测试
**/
@RunWith (AndroidJUnit4.class)
public class BaseServiceTest {
    private Context context;
    @Before
    public void setUp() {
        context = InstrumentationRegistry.getTargetContext();
    }
    @Test (expected = NullPointerException.class)
    public void onBind() throws Exception {
        final BaseService myService = new BaseService();
        context.startService(new Intent(context, BaseService.class));
        myService.onBind(new Intent());
    }
    @Test
    public void onStartCommand() throws Exception {
        final BaseService myService = new BaseService();
        context.startService(new Intent(context, BaseService.class));
        assertEquals(Service.START_STICKY, BaseService.onStartCommand(new Intent(), 0, 0));
    }
    @Test
    public void onCreate() throws Exception {
        final BaseService myService = new BaseService();
        context.startService(new Intent(context, BaseService.class));
        myService.onCreate();
        assertTrue(BaseService.isServiceStarted());
    }
    @Test
    public void onDestroy() throws Exception {
        final BaseService myService = new BaseService();
        context.startService(new Intent(context, BaseService.class));
        myService.onDestroy();
        assertFalse(BaseService.isServiceStarted());
    }
    }

参考资料与扩展阅读

Google官方测试支持库文档

Why is JUnit 4 on Android not working?

Lint in Studio 2.3

Android — How to test a Service

实战 - 如何测试 Service ?

技术点

RestrictTo注解

AndroidJUnitRunner

实战