如何使用Mockito模拟DisplayMetrics

Question

我有一个自定义视图，我正在尝试测试不同的屏幕尺寸，我无法找到有关如何在单元测试中正确模拟显示宽度的文档或示例。

这是我试图使用它的一个例子：

private CustomTextView customTV;

@Override
protected void setUp() throws Exception {
    super.setUp();

    DisplayMetrics displayMetrics = mock(DisplayMetrics.class);
    displayMetrics.widthPixels = 600;

    Resources mockResources = mock(Resources.class);
    when(mockResources.getDisplayMetrics()).thenReturn(displayMetrics);

    Context mockContext = mock(Context.class);
    when(mockContext.getResources()).thenReturn(mockResources);

    customTV = new CustomTextView(mockContext);
}

@SmallTest
public void testViewSize() {
    Assert.assertEquals("Text size did not scale", 42, customTV.getTextSize());
}

另外，我只在某些设备上出现错误（上述实现适用于某些屏幕尺寸，但不是全部）：

Error in testViewSize:
java.lang.NullPointerException: Attempt to invoke virtual method 'boolean android.content.res.Configuration.isLayoutSizeAtLeast(int)' on a null object reference
    at android.view.ViewConfiguration.<init>(ViewConfiguration.java:284)
    at android.view.ViewConfiguration.get(ViewConfiguration.java:364)
    at android.view.View.<init>(View.java:3781)
    at android.view.View.<init>(View.java:3876)
    at android.widget.TextView.<init>(TextView.java:655)
    at android.widget.TextView.<init>(TextView.java:650)
    at android.widget.TextView.<init>(TextView.java:646)
    at com.foo.bar.view.CustomTextView.<init>(CustomTextView.java:55)
    at com.foo.bar.view.CustomTextView.<init>(CustomTextView.java:45)
    at com.foo.bar.view.CustomTextViewTests.setUp(CustomTextViewTests.java:52)
    at android.test.AndroidTestRunner.runTest(AndroidTestRunner.java:191)
    at android.test.AndroidTestRunner.runTest(AndroidTestRunner.java:176)
    at android.test.InstrumentationTestRunner.onStart(InstrumentationTestRunner.java:557)
    at android.app.Instrumentation$InstrumentationThread.run(Instrumentation.java:1874)

我真正想做的就是将displayMetrics.widthPixels的返回值设置为一个特定的数字，但因为它不是方法调用，比如getter或setter，我不能像我在when和thenReturn方法那样覆盖它。其他模拟对象。

有没有更简单的方法来模拟Context / Resources / DisplayMetrics？

Answer 1

要回答你的问题，你就像你正在做的那样嘲笑它。

DisplayMetrics metrics = mock(DisplayMetrics.class);
metrics.widthPixels = 300;

Resources resources = mock(Resources.class);
when(resources.getDisplayMetrics()).thenReturn(metrics);

Assert.assertEquals(300, resources.getDisplayMetrics().widthPixels);
// ^^ see proof

您发布的错误消息只是建议您需要模拟更多对象。你做得不够。

java.lang.NullPointerException：尝试调用虚方法'boolean android.content.res.Configuration

所以也模拟了Configuration对象。

编辑：

如果您正在使用Robolectric，则使用实际配置显示的代码：

Context context = mock(Context.class);
Resources resources = mock(Resources.class);
when(resources.getConfiguration()).thenReturn(RuntimeEnvironment.application.getResources().getConfiguration());
when(context.getResources()).thenReturn(resources);

Answer 2

最后找到了两种不同的方法，这两种方法最多只能使用Mockito作为测试库。

选项1：更新真正的Context

private CustomTextView customTV;

@Override
protected void setUp() throws Exception {
    super.setUp();

    Context context = getContext();
    DisplayMetrics displayMetrics = context.getResources().getDisplayMetrics();

    Configuration config = context.getResources().getConfiguration();
    displayMetrics.widthPixels = 600;
    // can optionally set the screen density as well:
    displayMetrics.densityDpi = DisplayMetrics.DENSITY_MEDIUM;
    config.densityDpi = DisplayMetrics.DENSITY_MEDIUM;

    context.getResources().updateConfiguration(config, displayMetrics);

    customTV = new CustomTextView(mockContext);
}

@SmallTest
public void testViewSize() {
    Assert.assertEquals("Text size did not scale", 42, customTV.getTextSize());
}

选项2：使用ContextWrapper + Mockito.spy

private CustomTextView customTV;

@Override
protected void setUp() throws Exception {
    super.setUp();

    Context context = new ScreenWidthContextWrapper(getContext(), 600);

    customTV = new CustomTextView(context);
}

private class ScreenWidthContextWrapper extends ContextWrapper {
    private final DisplayMetrics mDisplayMetrics;
    private final Resources mSpyResources;

    public ScreenWidthContextWrapper(Context realContext, int widthPixels) {
        super(realContext);

        Resources realResources = realContext.getResources();

        mDisplayMetrics = new DisplayMetrics();
        mDisplayMetrics.widthPixels = widthPixels;
        mDisplayMetrics.setTo(realResources.getDisplayMetrics());

        mSpyResources = spy(realResources);
        when(mSpyResources.getDisplayMetrics()).thenReturn(mDisplayMetrics);
    }

    @Override
    public Resources getResources() {
        return mSpyResources;
    }
}

@SmallTest
public void testViewSize() {
    Assert.assertEquals("Text size did not scale", 42, customTV.getTextSize());
}