如何对与系统交互的方法进行单元测试（或 Android）类

Question

您如何设法编写与系统交互的单元测试类即 Android 框架类？

假设你有那些类:

public class DeviceInfo {
    public final int screenWidth, screenHeight;
    public final String model;

    public DeviceInfo(int screenWidth, int screenHeight, String deviceModel) {
        this.screenWidth = screenWidth;
        this.screenHeight = screenHeight;
        this.model = deviceModel;
    }

}

public class DeviceInfoProvider {
    private final Context context;

    public DeviceInfoProvider(Context context) {
        this.context = context;
    }

    public DeviceInfo getScreenParams() {
        DisplayMetrics metrics = new DisplayMetrics();
        WindowManager windowManager = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
        windowManager.getDefaultDisplay().getMetrics(metrics);
        int screenWidth = metrics.widthPixels;
        int screenHeight = metrics.heightPixels;
        String model= Build.MODEL;
        DeviceInfo params = new DeviceInfo(screenWidth, screenHeight, model);
        return params;
    }
}

如何编写测试来验证方法 DeviceInfoProvider.getScreenParams() 的正确行为。

以下测试通过，但它非常丑陋和脆弱：

@Test
public void testGetScreenParams() throws Exception {
    // Setup
    Context context = spy(RuntimeEnvironment.application);
    DeviceInfoProvider deviceInfoProvider = new DeviceInfoProvider(context);

    // Stub
    WindowManager mockWindowManager = mock(WindowManager.class);
    Display mockDisplay = mock(Display.class);
    when(context.getSystemService(Context.WINDOW_SERVICE)).thenReturn(mockWindowManager);
    when(mockWindowManager.getDefaultDisplay()).thenReturn(mockDisplay);
    doAnswer(new Answer() {
        @Override
        public Object answer(InvocationOnMock invocation) throws Throwable {
            DisplayMetrics metrics = (DisplayMetrics) invocation.getArguments()[0];
            metrics.scaledDensity = 3.25f;
            metrics.widthPixels = 1081;
            metrics.heightPixels = 1921;
            return null;
        }
    }).when(mockDisplay).getMetrics(any(DisplayMetrics.class));

    // Run
    DeviceInfo deviceInfo = deviceInfoProvider.getScreenParams();

    // Verify
    assertThat(deviceInfo.screenWidth, equalTo(1081));
    assertThat(deviceInfo.screenHeight, equalTo(1921));
    assertThat(deviceInfo.model, equalTo(Build.MODEL));
}

你会如何改进它？

注意：目前我正在使用 Robolectric、Mockito 和 PowerMock

Answer 1

被测系统与实现问题的耦合过于紧密。尽量避免嘲笑你不拥有的 classes。抽象接口背后的代码并将责任委托给在运行时间恰好在接口背后的任何实现。

public interface DisplayProvider {
    public int widthPixels;
    public int heightPixels;
}

public interface BuildProvider {
    public string Model;
}

重构依赖 class 以依赖抽象而非具体化（实现问题）。

public class DeviceInfoProvider {
    private final DisplayProvider display;
    private final BuildProvider build;

    public DeviceInfoProvider(DisplayProvider display, BuildProvider build) {
        this.display = display;
        this.build = build;
    }

    public DeviceInfo getScreenParams() {
        int screenWidth = display.widthPixels;
        int screenHeight = display.heightPixels;
        String model = build.Model;
        DeviceInfo params = new DeviceInfo(screenWidth, screenHeight, model);
        return params;
    }
}

孤立的单元测试

@Test
public void testGetScreenParams() throws Exception {
    // Arrange
    DisplayProvider mockDisplay = mock(DisplayProvider.class);
    BuildProvider mockBuild = mock(BuildProvider.class);        
    DeviceInfoProvider deviceInfoProvider = new DeviceInfoProvider(mockDisplay, mockBuild);

    when(mockDisplay.widthPixels).thenReturn(1081);
    when(mockDisplay.heightPixels).thenReturn(1921);
    when(mockBuild.Model).thenReturn(Build.MODEL);

    // Act
    DeviceInfo deviceInfo = deviceInfoProvider.getScreenParams();

    // Assert
    assertThat(deviceInfo.screenWidth, equalTo(1081));
    assertThat(deviceInfo.screenHeight, equalTo(1921));
    assertThat(deviceInfo.model, equalTo(Build.MODEL));
}

如何对与系统交互的方法进行单元测试（或 Android）类

How to unit test methods that interact with System (or Android) classes

java

android

unit-testing

mockito

powermock