Espresso 定制匹配器

默认情况下，Espresso 有许多匹配器，可帮助你查找进行某些检查或与之交互所需的视图。

最重要的可以在以下备忘单中找到：

https://google.github.io/android-testing-support-library/docs/espresso/cheatsheet/

匹配器的一些示例是：

• withId（R.id.ID_of_object_you_are_looking_for）;
• withText（你希望对象有一些文字）;
• isDisplayed()< - check 是可见的视图
• doesNotExist()< - 检查视图是否不存在

所有这些对于日常使用都非常有用，但如果你有更复杂的视图编写自定义匹配器可以使测试更具可读性，你可以在不同的地方重用它们。

你可以扩展 2 种最常见的匹配器类型： TypeSafeMatcher BoundedMatcher

实现 TypeSafeMatcher 要求你检查实例是否为你要断言的视图，如果它是正确的类型，你将其某些属性与你提供给匹配器的值相匹配。

例如，类型安全匹配器验证图像视图具有正确的 drawable：

public class DrawableMatcher extends TypeSafeMatcher<View> {

    private @DrawableRes final int expectedId;
    String resourceName;
    
    public DrawableMatcher(@DrawableRes int expectedId) {
        super(View.class);
        this.expectedId = expectedId;
    }

    @Override
    protected boolean matchesSafely(View target) {
        //Type check we need to do in TypeSafeMatcher
        if (!(target instanceof ImageView)) {
            return false;
        }
        //We fetch the image view from the focused view
        ImageView imageView = (ImageView) target;
        if (expectedId < 0) {
            return imageView.getDrawable() == null;
        }
        //We get the drawable from the resources that we are going to compare with image view source
        Resources resources = target.getContext().getResources();
        Drawable expectedDrawable = resources.getDrawable(expectedId);
        resourceName = resources.getResourceEntryName(expectedId);

        if (expectedDrawable == null) {
            return false;
        }
        //comparing the bitmaps should give results of the matcher if they are equal
        Bitmap bitmap = ((BitmapDrawable) imageView.getDrawable()).getBitmap();
        Bitmap otherBitmap = ((BitmapDrawable) expectedDrawable).getBitmap();
        return bitmap.sameAs(otherBitmap);
    }

    @Override
    public void describeTo(Description description) {
        description.appendText("with drawable from resource id: ");
        description.appendValue(expectedId);
        if (resourceName != null) {
            description.appendText("[");
            description.appendText(resourceName);
            description.appendText("]");
        }
    }
}

匹配器的用法可以像这样包装：

  public static Matcher<View> withDrawable(final int resourceId) {
    return new DrawableMatcher(resourceId);
}

 onView(withDrawable(R.drawable.someDrawable)).check(matches(isDisplayed()));

有界匹配器类似于你不需要进行类型检查，但是，因为这是自动完成的：

 /**
 * Matches a {@link TextInputFormView}'s input hint with the given resource ID
 *
 * @param stringId
 * @return
 */
public static Matcher<View> withTextInputHint(@StringRes final int stringId) {
    return new BoundedMatcher<View, TextInputFormView>(TextInputFormView.class) {
        private String mResourceName = null;

        @Override
        public void describeTo(final Description description) {
            //fill these out properly so your logging and error reporting is more clear
            description.appendText("with TextInputFormView that has hint ");
            description.appendValue(stringId);
            if (null != mResourceName) {
                description.appendText("[");
                description.appendText(mResourceName);
                description.appendText("]");
            }
        }

        @Override
        public boolean matchesSafely(final TextInputFormView view) {
            if (null == mResourceName) {
                try {
                    mResourceName = view.getResources().getResourceEntryName(stringId);
                } catch (Resources.NotFoundException e) {
                    throw new IllegalStateException("could not find string with ID " + stringId, e);
                }
            }
            return view.getResources().getString(stringId).equals(view.getHint());
        }
    };
}

有关匹配器的更多信息，请阅读：

http://hamcrest.org/

https://developer.android.com/reference/android/support/test/espresso/matcher/ViewMatchers.html